# Canine Cardiac Auscultation: Murmur Grading and Diagnostic Approach


## Key Takeaways

- Cardiac auscultation is a fundamental screening tool for canine heart disease, identifying turbulent blood flow, but does not provide a definitive diagnosis; murmur characteristics (timing, location, intensity, quality) narrow differential diagnoses.
- The 0-6 grading scale quantifies murmur intensity, with Grade 1 being very soft and Grade 6 audible without stethoscope contact, but intensity does not directly correlate with disease severity; a palpable precordial thrill is associated with Grade 4 murmurs and above.
- Innocent murmurs in puppies are typically soft (Grade 1-3), short, early to mid-systolic, and best heard at the left heart base, whereas diastolic or continuous murmurs, and systolic murmurs exceeding 80% of systole, warrant prompt echocardiography.
- A systematic auscultation technique, including listening at specific valve areas (left apex, left base, right fourth intercostal space) for at least 15-30 seconds with both diaphragm and bell, is crucial for accurate detection and characterization.
- Electronic stethoscopes and digital phonocardiography can enhance murmur detection and improve inter-observer agreement, particularly for less experienced clinicians, by providing amplified sound and visual waveform analysis.
- A normal cardiac auscultation does not exclude structural heart disease, as evidenced by studies showing valvular regurgitation in dogs with no audible murmur, underscoring the need for echocardiography in specific clinical scenarios.

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Cardiac auscultation remains the first and most accessible screening tool for canine heart disease. This article provides a systematic framework for performing auscultation, characterizing murmurs, and applying murmur grade and quality to guide diagnostic decisions. It is written for veterinary students and practitioners who want to move beyond pattern recognition toward structured clinical reasoning. The focus is on technique and interpretation, not treatment.

The clinical question this article answers is direct: when you hear a murmur in a dog, what exactly have you detected, how reliably have you detected it, and what does that finding obligate you to do next? Auscultation identifies a physical event, turbulent blood flow, but it does not by itself establish a diagnosis. The murmur's timing, location, intensity, and quality narrow the differential list, while signalment and physical examination findings determine whether the murmur is likely innocent, hemodynamically significant, or an incidental finding in a dog with unrelated disease.

## At a Glance

| Parameter | Decision or Fact |
|---|---|
| Murmur grade | Use the 0 to 6 scale, grade reflects intensity, not severity of disease |
| Grade 1 murmur | Very soft, heard only after focused listening in a quiet room |
| Grade 3 murmur | Moderate intensity, readily heard, no palpable thrill |
| Grade 4 murmur | Loud, associated with a palpable precordial thrill |
| Systolic timing | Most canine murmurs are systolic, diastolic murmurs are uncommon and warrant prompt echocardiography |
| Innocent murmur | Typically grade 1 to 3, short, early to mid-systolic, left basilar, in puppies |
| Electronic stethoscope | May improve murmur detection, especially for less experienced auscultators |
| Auscultation limitation | Normal auscultation does not exclude structural heart disease |

## Physiology of Murmur Generation

Murmurs arise from turbulent blood flow, which occurs when the velocity of flow exceeds a critical threshold, when flow passes through a narrowed orifice, when it regurgitates through an incompetent valve, or when it flows into a dilated chamber. The intensity of a murmur depends on the pressure gradient driving flow, the volume of flow, and the distance between the source and the stethoscope chest piece. A thin-chested dog with a high-output state may produce an audible murmur from trivial regurgitation, while an obese or heavily muscled dog may mask a hemodynamically significant lesion.

The cardiac cycle determines when murmurs occur. Systolic murmurs appear between S1 and S2 and include ejection murmurs, regurgitant murmurs of mitral or tricuspid insufficiency, and murmurs associated with ventricular septal defects. Diastolic murmurs appear between S2 and the next S1 and include aortic or pulmonic insufficiency and mitral stenosis. Continuous murmurs span S1 and S2, as seen with patent ductus arteriosus. Timing alone does not establish etiology, but it sharply narrows the differential.

## Auscultation Technique

Auscultation requires a quiet room, a cooperative patient, and a systematic approach. The dog should stand, and the examiner should approach from the right side for right-sided auscultation and the left side for left-sided auscultation. The stethoscope chest piece should be placed directly on the thoracic wall, not over the triceps or the shoulder. The left hemithorax is examined over the cardiac apex, the mitral valve area at the fifth to sixth intercostal space near the costochondral junction, and the aortic and pulmonic valve areas at the fourth to third intercostal spaces near the sternum. The right hemithorax is examined over the tricuspid valve area at the fourth to fifth intercostal space.

The examiner should listen with both the diaphragm and the bell. The diaphragm is better suited for higher-frequency sounds, including most murmurs, while the bell may accentuate lower-frequency gallops or the third heart sound. Each valve area should be auscultated for at least 15 to 30 seconds, and the heart rate and rhythm should be noted concurrently. The femoral pulse should be palpated simultaneously to correlate pulse quality with cardiac auscultation.

Observer experience materially affects diagnostic accuracy. In a comparison of conventional and sensor-based electronic stethoscopes, a final-year veterinary student correctly detected murmurs in 20 of 27 suspected cases with a traditional stethoscope, while an experienced clinician detected 25 of 27. Both observers improved with the electronic stethoscope, the student to 26 of 27 and the clinician to 27 of 27. The agreement between observers on murmur intensity grading was highly significant for both instruments. These findings support the use of electronic stethoscopes as a teaching tool and as an aid for less experienced auscultators, but they also underscore that auscultation skill is acquired and calibrated through repeated comparison with echocardiographic findings.

## Murmur Grading Systems

The standard grading system in veterinary medicine is the 0 to 6 scale, in which grade 1 is a very soft murmur heard only after focused listening, grade 2 is soft but readily heard, grade 3 is moderate intensity without a thrill, grade 4 is loud with a palpable precordial thrill, grade 5 is very loud with a thrill and is heard when the stethoscope is barely lifted off the chest wall, and grade 6 is audible without the stethoscope touching the chest. The scale is ordinal, not linear. A grade 4 murmur is not twice as loud as a grade 2 murmur, and the grade does not correlate directly with the severity of the underlying lesion.

A simplified 0 to 3 scale has been proposed and studied. In a phonocardiographic study of 20 dogs, observers' gradings on the traditional 0 to 6 scale correlated significantly with gradings on the 0 to 3 scale, with correlation coefficients ranging from 0.640 to 0.908. The simplified scale may be easier for novices to apply consistently, but the 0 to 6 scale remains the clinical standard and should be used in the medical record.

## Murmur Characterization

Beyond grade, the clinician must characterize a murmur by timing, location, radiation, and quality. Timing is determined by the relationship to S1 and S2. Location is the point of maximal intensity. Radiation describes where the murmur is heard beyond that point. Quality includes descriptors such as plateau, crescendo-decrescendo, decrescendo, musical, or harsh.

Phonocardiography can improve the objectivity of murmur characterization. In the same study of 20 dogs, four observers with varying experience showed only minimal differences, 95% to 100% agreement, in analyzing murmur intensity and quality when they listened to recordings while viewing digital phonocardiograms. This suggests that visual correlation with the cardiac cycle improves consistency, a principle that can be applied in teaching settings.

## Innocent Versus Pathologic Murmurs

Innocent murmurs are common in puppies and are typically grade 1 to 3, short, early to mid-systolic, and best heard over the left heart base. They are caused by physiologic turbulence in a normal heart, often related to high cardiac output or small chamber dimensions. A study of 186 asymptomatic puppies found that murmurs longer than 80% of systole are most likely abnormal, a useful threshold for distinguishing innocent from pathologic murmurs. The same study found that plasma NT-proBNP concentrations did not differentiate puppies with innocent murmurs from those without murmurs, and that normal NT-proBNP levels did not rule out congenital anomalies. Auscultation and phonocardiography therefore remain the first-line tools, with echocardiography as the definitive test.

The absence of a murmur does not exclude structural heart disease. In a cohort of 40 middle-aged dogs with no history of cardiac pathology, Doppler echocardiography identified valvular regurgitation in 11 dogs, and only one of these had an audible murmur on standard examination. This dissociation between auscultatory findings and echocardiographic disease is an important limitation of auscultation as a screening tool, particularly in older large-breed dogs.

## Structured Auscultation Protocol for the Clinical Encounter

Auscultation should follow a fixed sequence so that no cardiac region is omitted and so that findings can be compared across examinations. Begin with the dog standing and quiet, with the thoracic wall accessible from both sides. Palpate the apex beat first to locate the point of maximal impulse, then place the stethoscope over the left fifth to sixth intercostal space near the costochondral junction. Sweep dorsally and cranially to the left heart base, then repeat the process on the right hemithorax. The right fourth intercostal space is the optimal window for tricuspid valve sounds and right-sided murmurs.

Each valve region should be auscultated for at least two full respiratory cycles. Ask an assistant to occlude the nostrils briefly if tachypnoea obscures cardiac sounds, but do not maintain occlusion long enough to induce distress. In obese dogs or those with deep chests, firm stethoscope pressure and repositioning of the forelimb forward may improve acoustic transmission. Muffled sounds that do not clarify with repositioning should be documented as such instead of forced into a grade.

Electronic stethoscopes with sensor-based amplification improve murmur detection compared with conventional acoustic instruments. In a comparative study of 21 dogs referred for suspected murmurs, an experienced clinician detected 25 of 27 murmurs with a traditional stethoscope and all 27 with an electronic device, while a final-year student detected 20 of 27 with the traditional instrument and 26 of 27 with the electronic one [Comparison of conventional and sensor-based electronic stethoscopes in detecting](https://pubmed.ncbi.nlm.nih.gov/22526814/)(https://pubmed.ncbi.nlm.nih.gov/22526814/). The student's agreement with the final diagnosis improved from fair to substantial when using the electronic stethoscope. Practices that see a high volume of cardiac patients should consider electronic auscultation as a standard tool, particularly when less experienced clinicians perform the initial examination.

Digital phonocardiography adds a visual component to auscultation. In a study of 20 dogs, four observers with differing experience levels showed only minimal differences in judging murmur intensity and quality when they listened to recordings while viewing digital phonocardiograms, despite significant disagreement during blind auscultation alone [Sound recording and digital phonocardiography of cardiac murmurs in](https://pubmed.ncbi.nlm.nih.gov/21354939/)(https://pubmed.ncbi.nlm.nih.gov/21354939/). Recording murmurs for later review, or for review by a cardiologist, reduces inter-observer variability and creates a permanent record that can be compared with future examinations.

## Decision Point: When Auscultation Findings Are Equivocal

A soft systolic murmur in a young puppy presents a common diagnostic fork. The clinician must decide between a diagnosis of innocent flow murmur and referral for echocardiography. Duration of the murmur is the most useful auscultatory discriminator. Murmurs that occupy more than 80 percent of systole are most likely pathologic, and puppies with such murmurs should be referred for echocardiography instead of monitored [N-Terminal Pro-B-Type Natriuretic Peptide and Phonocardiography in Differentiating Innocent](https://pubmed.ncbi.nlm.nih.gov/28316101/)(https://pubmed.ncbi.nlm.nih.gov/28316101/). Innocent murmurs are typically early systolic, soft, and localized to the left base.

Location and radiation pattern also guide the decision. A murmur heard maximally over the left heart base that radiates cranially along the great vessels suggests aortic or pulmonic outflow disease. A murmur loudest at the left apex is more consistent with mitral regurgitation. Right-sided murmurs, particularly those loudest over the right fourth intercostal space, raise suspicion for tricuspid dysplasia or a ventricular septal defect. Continuous murmurs are always pathologic and warrant prompt echocardiographic evaluation.

Signalment modifies the pretest probability. A grade 2 left basilar systolic murmur in a 10-week-old Cavalier King Charles Spaniel is more likely to be innocent than the same murmur in a 10-week-old Boxer, where pulmonic stenosis is common. Conversely, a grade 3 apical systolic murmur in a 12-year-old small-breed dog is most likely myxomatous mitral valve disease, and the question is not whether disease exists but how severe it has become.

## Murmur Grading and Clinical Significance

The traditional six-point grading scale remains the standard for clinical communication. Grade 1 murmurs are barely audible, requiring focused attention. Grade 2 murmurs are soft but immediately audible. Grade 3 murmurs are moderately loud without a palpable thrill. Grade 4 murmurs are loud with a palpable precordial thrill. Grade 5 murmurs are very loud, palpable, and audible with the stethoscope rim just lifted off the chest wall. Grade 6 murmurs are audible with the stethoscope completely off the chest.

A simplified three-point scale has been proposed as an alternative, and studies show significant correlation between the two systems, with correlation coefficients ranging from 0.640 to 0.908 across observers [Sound recording and digital phonocardiography of cardiac murmurs in](https://pubmed.ncbi.nlm.nih.gov/21354939/)(https://pubmed.ncbi.nlm.nih.gov/21354939/). The three-point scale may be easier for novices to apply consistently, but the six-point scale remains the expected standard in referral communications and medical records.

| Murmur Grade | Auscultatory Finding | Typical Clinical Significance | Recommended Action |
|---|---|---|---|
| 1 | Barely audible, localized | Often innocent or very early disease | Recheck in 3 to 6 months |
| 2 | Soft, immediately audible | Innocent or mild structural disease | Characterize further, consider echocardiography if risk factors present |
| 3 | Moderate intensity, no thrill | Structural disease likely | Echocardiography recommended |
| 4 | Loud, palpable thrill | Significant structural disease | Echocardiography indicated |
| 5 | Very loud, audible with rim off chest | Severe disease | Echocardiography indicated, assess for congestive heart failure |
| 6 | Audible with stethoscope off chest | Severe disease | Echocardiography indicated, assess for congestive heart failure |

Grade alone does not predict the specific lesion. A grade 4 murmur can arise from a small ventricular septal defect with high flow velocity or from severe mitral regurgitation. The grade reflects the intensity of the sound generated, which depends on flow velocity, the pressure gradient across the orifice, and the distance between the source and the chest wall. Obesity, pleural effusion, and pericardial effusion all attenuate murmur intensity, so a grade 2 murmur in an obese dog may represent more significant disease than the same grade in a lean dog.

## Diagnostic Decision Tree for Echocardiography

Echocardiography is the definitive diagnostic test for structural heart disease, but it is not required for every dog with a murmur. The decision to pursue imaging depends on the murmur characteriztics, the signalment, the presence of clinical signs, and the availability of a cardiologist or experienced ultrasonographer.

Refer for echocardiography when any of the following criteria are met:

- Murmur grade 3 or higher
- Murmur duration exceeding 80 percent of systole
- Any diastolic murmur
- Any continuous murmur
- Murmur loudest over the right hemithorax
- Murmur in a breed predisposed to congenital disease
- Murmur accompanied by clinical signs such as cough, syncope, exercise intolerance, or respiratory distress
- Murmur that increases in grade between examinations
- Murmur in a dog with arrhythmia or pulse deficits

Auscultation alone will miss a substantial proportion of structural disease. In a screening study of 40 middle-aged dogs with no history of cardiac pathology, Doppler echocardiography identified valvular regurgitation in 11 dogs, and seven of these cases were severe enough to warrant exclusion from a clinical trial, yet only one of the 11 had an audible murmur [Asymptomatic heart valve dysfunction in healthy middle-aged companion dogs](https://pubmed.ncbi.nlm.nih.gov/28299636/)(https://pubmed.ncbi.nlm.nih.gov/28299636/). This finding has two implications. First, a normal cardiac auscultation does not exclude structural heart disease. Second, screening echocardiography should be considered in middle-aged and older dogs before anesthesia, before starting cardiotoxic chemotherapy, or when the dog is intended for breeding.

The absence of a murmur in a dog with suspected cardiac disease should prompt consideration of other diagnostic tools. Thoracic radiography can identify cardiomegaly, pulmonary edema, and pleural effusion. Electrocardiography detects arrhythmias and chamber enlargement patterns. Point-of-care NT-proBNP assays can support the presence of clinically relevant heart disease, although a negative result does not exclude it. These biomarkers have been studied most extensively in cats, where a point-of-care assay showed 43 percent sensitivity and 96 percent specificity for detecting echocardiographic abnormalities in apparently healthy cats [Point-of-care N-terminal pro B-type natriuretic peptide assay to screen](https://pubmed.ncbi.nlm.nih.gov/33993546/)(https://pubmed.ncbi.nlm.nih.gov/33993546/). The same principle applies to dogs: a positive result supports the decision to pursue echocardiography, while a negative result does not rule out disease.

## Documentation and Longitudinal Monitoring

Every auscultatory finding should be recorded in a standardized format that permits comparison with future examinations. The record should include the murmur grade, the point of maximal intensity, the timing within the cardiac cycle, the duration relative to systole, the presence or absence of a thrill, and the heart rate and rhythm at the time of examination. A phonocardiogram, when available, provides an objective record that removes observer bias from the comparison.

For dogs with confirmed or suspected myxomatous mitral valve disease, the murmur grade should be tracked at each visit. Progression from grade 2 to grade 3, or the new appearance of a thrill, may signal hemodynamic deterioration that warrants thoracic radiography and a reassessment of the treatment plan. The interval between rechecks depends on the murmur grade and the presence of clinical signs. A dog with a stable grade 2 murmur and no clinical signs can be rechecked in six months. A dog with a grade 4 murmur and a new cough should be evaluated within days.

The clinical context determines how aggressively a murmur is investigated. A grade 2 murmur in a 14-year-old Dachshund with no clinical signs may reasonably be monitored without echocardiography, particularly if the owners decline intervention. The same murmur in a 6-year-old Boxer intended for breeding warrants full investigation. The decision framework presented here is a guide, not a substitute for clinical judgment, and the owner's goals and financial constraints are legitimate considerations in the diagnostic plan.

## Recognized Complications and Failure Modes

The most consequential failure in canine cardiac auscultation is the false negative, where a clinically significant murmur is missed entirely. This occurs most often with soft murmurs, high-frequency murmurs, or murmurs in patients with tachycardia. In one comparative study, a final-year student detected only 74% of confirmed murmurs with a traditional stethoscope, while an experienced clinician detected 92.6% with the same instrument, and both observers improved with a sensor-based electronic stethoscope ([comparison of conventional and sensor-based electronic stethoscopes](https://pubmed.ncbi.nlm.nih.gov/22526814/)). The lesson is not that electronic stethoscopes are mandatory, but that operator experience and deliberate technique materially change detection rates.

The converse failure, the false positive, occurs when normal physiologic sounds are misclassified as murmurs. Respiratory sounds, particularly in panting dogs, and the normal first and second heart sounds in thin-chested breeds are common sources. A murmur must be sustained, occupy a consistent portion of the cardiac cycle, and persist across multiple cardiac cycles to be considered genuine.

A third failure mode is mischaracterisation instead of misdetection. A murmur that is correctly heard but incorrectly graded for intensity, timing, or point of maximal intensity can misdirect the entire diagnostic plan. Observer agreement on murmur quality is poor even among experienced clinicians, though agreement improves substantially when phonocardiographic tracings are reviewed alongside the audio recording ([sound recording and digital phonocardiography of cardiac murmurs in dogs](https://pubmed.ncbi.nlm.nih.gov/21354939/)).

| Observation | Likely cause | Discriminating check |
|---|---|---|
| Murmur heard at one visit, absent at next | Physiologic variation in heart rate or output, or auscultation error | Re-auscultate in a quiet room with the dog restrained in standing position, compare grade against the documented baseline |
| Systolic murmur that disappears when the dog stops panting | Respiratory sound mistaken for a murmur | Listen for at least 10 consecutive cycles, a true murmur persists in expiration |
| Murmur audible only with the bell | Low-frequency murmur, or observer using the diaphragm exclusively | Repeat with both chest pieces, document which piece detected the sound |
| Grade III murmur with no echocardiographic lesion | Overgrading, or dynamic outflow tract murmur | Correlate with Doppler echocardiography, consider repeat auscultation by a second observer |
| Murmur intensity changes between examinations | Progression of disease, or observer inconsistency | Use the same stethoscope, same room, and same patient position for serial examinations |

## Common Errors and Corrective Actions

Students and less experienced clinicians most often err in three areas. First, they grade intensity before they have identified timing. The grade is assigned after the murmur is fully characterized, not before. Second, they auscultate too briefly. A minimum of 30 seconds at each valve site, in a quiet room, is required for reliable characterization. Third, they fail to integrate the murmur with the remainder of the physical examination. A grade II left apical systolic murmur in a 12-year-old Cavalier King Charles Spaniel with a normal femoral pulse and no cough carries a different weight than the same murmur in a dyspnoeic dog with weak pulses.

The corrective action for each is procedural. Grade after characterization. Auscultate systematically, moving from the apex to the base, then repeat with the dog in a different position. Always pair auscultation with palpation of the femoral pulse and assessment of mucous membrane color and capillary refill time. The electronic stethoscope with phonocardiographic display reduces inter-observer variability in grading, but it does not replace clinical judgment ([sound recording and digital phonocardiography of cardiac murmurs in dogs](https://pubmed.ncbi.nlm.nih.gov/21354939/)).

## Limitations of the Evidence and Areas of Expert Disagreement

The evidence base for canine murmur grading rests on small studies with modest sample sizes. The studies cited here enrolled 20 to 40 dogs, and their findings on observer agreement and electronic stethoscope utility may not generalize to all practice settings ([comparison of conventional and sensor-based electronic stethoscopes](https://pubmed.ncbi.nlm.nih.gov/22526814/)). The correlation between auscultatory grade and echocardiographic severity is imperfect. In one cohort of middle-aged dogs with echocardiographically confirmed valvular regurgitation, only one of eleven affected dogs had an audible murmur on standard examination ([asymptomatic heart valve dysfunction in healthy middle-aged companion dogs](https://pubmed.ncbi.nlm.nih.gov/28299636/)). This finding underscores that auscultation is a screening tool, not a definitive diagnostic modality.

Expert opinion still differs on the threshold for echocardiography in asymptomatic dogs with a soft left apical systolic murmur. Some cardiologists recommend echocardiography for any murmur in a puppy, while others reserve it for murmurs that are grade III or higher, or that persist beyond 16 weeks of age. In puppies, phonocardiographic findings can help distinguish innocent from pathologic murmurs, with murmurs occupying more than 80% of systole most likely abnormal ([NT-proBNP and phonocardiography in differentiating innocent cardiac murmurs from congenital cardiac anomalies](https://pubmed.ncbi.nlm.nih.gov/28316101/)). The same study found that plasma NT-proBNP within the reference range does not exclude congenital heart disease, so biomarker testing cannot replace echocardiography when clinical suspicion is high.

## Referral, Laboratory Involvement, and Reporting

Referral to a cardiologist is warranted when a murmur is accompanied by clinical signs such as syncope, exercise intolerance, respiratory distress, or ascites, when a murmur is grade III or higher, when a murmur is identified in a puppy and persists beyond 16 weeks of age, or when the clinician is uncertain whether a murmur is innocent or pathologic. Echocardiography is the definitive diagnostic test and should not be delayed when these criteria are met.

Laboratory involvement is adjunctive. Point-of-care NT-proBNP can support decision-making, but a negative result does not rule out structural heart disease, and a positive result should prompt echocardiography instead of treatment ([point-of-care NT-proBNP assay to screen apparently healthy cats for cardiac disease](https://pubmed.ncbi.nlm.nih.gov/33993546/)). This finding, though derived from feline patients, reflects the general principle that biomarkers supplement, but do not replace, imaging.

Regulatory reporting is rarely relevant to canine cardiac murmurs. Breeders may request certification of cardiac status for breeding programs, and some jurisdictions have specific requirements for working dogs. The [AVMA practice resources](https://www.avma.org/resources-tools) provide guidance on professional documentation standards. Where export or interstate movement of a dog with known cardiac disease is contemplated, the [WOAH terrestrial animal health standards](https://www.woah.org/en/what-we-do/standards/codes-and-manuals/terrestrial-code-online-access/) may apply, though companion animal transport is generally governed by national instead of international rules.

## Frequently Asked Questions

### How should I proceed when only a traditional acoustic stethoscope is available?

A traditional acoustic stethoscope remains a valid primary tool. An experienced clinician detected murmurs correctly in 25 of 27 suspected cases using a conventional stethoscope, while a final-year student detected 20 of 27, as reported in a [comparison of conventional and sensor-based electronic stethoscopes](https://pubmed.ncbi.nlm.nih.gov/22526814/). The electronic device improved the student's detection to 26 of 27. If you rely on an acoustic stethoscope, compensate by spending more time in a quiet room, using a consistent systematic protocol, and seeking a second opinion for equivocal findings. Digital phonocardiography, when available, offers the advantage of objective waveform review and can be re-examined after the patient leaves.

### When is echocardiography truly necessary versus optional?

Echocardiography is indicated when a murmur is loud, diastolic, continuous, or accompanied by clinical signs such as syncope, respiratory distress, or weak femoral pulses. It is also warranted when a murmur fails to resolve by 6 months of age in a puppy, since [phonocardiographic studies in asymptomatic puppies](https://pubmed.ncbi.nlm.nih.gov/28316101/) show that murmurs occupying more than 80% of systole are most likely abnormal. For a soft, grade 1 to 2 left apical systolic murmur in an otherwise healthy adult dog, echocardiography can be deferred with recheck in 6 months. Remember that auscultation can miss significant disease: in one [screening study of middle-aged dogs](https://pubmed.ncbi.nlm.nih.gov/28299636/), only one of eleven dogs with echocardiographic valvular regurgitation had an audible murmur.

### How do I explain the limitations of auscultation to an owner?

Owners often assume a normal heart sounds examination means a healthy heart. Explain that auscultation detects murmurs, which are audible turbulence, but cannot measure valve thickness, chamber size, or contractility. Cite the [screening study of asymptomatic middle-aged dogs](https://pubmed.ncbi.nlm.nih.gov/28299636/) as evidence that echocardiography can reveal regurgitation in dogs with no audible murmur. Frame the murmur as a finding that increases the probability of structural disease, not as a diagnosis itself. If you recommend echocardiography, describe it as the definitive test that will guide whether medication or monitoring is appropriate. If you do not recommend it, state the specific recheck interval and the clinical signs that should prompt earlier evaluation.

### What should I record in the medical record beyond the grade?

Record the grade using the six-point scale, the point of maximal intensity, timing in the cardiac cycle, and response to positional change. Note the dog's signalment, heart rate, rhythm, and pulse quality at the same examination. Document whether the murmur was present at the first visit or is new, and record the ambient noise level if it was suboptimal. Include your recommendation, whether that is echocardiography, recheck in 3 to 6 months, or referral, and state the specific criteria that would change that plan. This longitudinal documentation is essential because a stable grade over serial examinations supports a benign process, while progressive intensification or new clinical signs should trigger escalation.

### Does the grading scale differ between dogs and other species?

The six-point scale is used across species, but the clinical thresholds differ. In cattle, for example, auscultation is the most useful tool for differentiating endocarditis, pericarditis, and congenital defects, as described in a [retrospective study of cardiac disease in cattle](https://pubmed.ncbi.nlm.nih.gov/18453376/). Pericarditis typically produces muffled sounds instead of a murmur, while endocarditis and congenital defects produce murmurs. In cats, murmurs are often dynamic and may be absent at rest despite structural disease, so a normal examination carries less negative predictive value. Always interpret the murmur grade within the species-specific differential diagnosis and the patient's signalment instead of applying a dog-derived algorithm to other species.

### How should I handle a murmur detected during a wellness visit when the owner declines referral?

Respect the owner's decision while ensuring they understand the trade-off. Document the murmur characteriztics, your recommendation, and the owner's choice in the record. Offer a compromise: a serum NT-proBNP measurement, which in [feline screening studies](https://pubmed.ncbi.nlm.nih.gov/33993546/) has high specificity but limited sensitivity, meaning a positive result supports cardiac disease while a negative result does not exclude it. Apply the same reasoning to dogs, where biomarker results must be interpreted alongside auscultation. Schedule a recheck in 3 to 6 months and ask the owner to monitor for exercise intolerance, cough, or syncope. If the murmur intensifies or clinical signs appear, revisit the referral discussion with concrete evidence of progression.

## Related Clinical & Scientific Guides

* [Canine Respiratory System: Anatomy and Physiology](/knowledge/veterinary-medicine/veterinary-anatomy-physiology/canine-respiratory-system-anatomy-physiology)
* [Comparative Anatomy of the Mammalian Kidney](/knowledge/veterinary-medicine/veterinary-anatomy-physiology/comparative-anatomy-mammalian-kidney)
* [Feline Cardiopulmonary Physiology: Heart-Lung Interactions](/knowledge/veterinary-medicine/veterinary-anatomy-physiology/feline-cardiopulmonary-physiology-heart-lung-interactions)


## References and Further Reading

- [Sound recording and digital phonocardiography of cardiac murmurs in dogs by using a sensor-based electronic stethoscope.](https://pubmed.ncbi.nlm.nih.gov/21354939/). 2011.
- [Comparison of conventional and sensor-based electronic stethoscopes in detecting cardiac murmurs of dogs.](https://pubmed.ncbi.nlm.nih.gov/22526814/). 2012.
- [N-Terminal Pro-B-Type Natriuretic Peptide and Phonocardiography in Differentiating Innocent Cardiac Murmurs from Congenital Cardiac Anomalies in Asymptomatic Puppies.](https://pubmed.ncbi.nlm.nih.gov/28316101/). 2017.
- [Clinicopathological presentation of cardiac disease in cattle and its impact on decision making.](https://pubmed.ncbi.nlm.nih.gov/18453376/). 2008.
- [Point-of-care N-terminal pro B-type natriuretic peptide assay to screen apparently healthy cats for cardiac disease in general practice.](https://pubmed.ncbi.nlm.nih.gov/33993546/). 2021.
- [Asymptomatic heart valve dysfunction in healthy middle-aged companion dogs and its implications for cardiac aging.](https://pubmed.ncbi.nlm.nih.gov/28299636/). 2017.
- [NCBI Bookshelf: Veterinary and Comparative Biomedical Sciences](https://www.ncbi.nlm.nih.gov/books/). NCBI Bookshelf.
- [MSD Veterinary Manual, Professional Edition](https://www.msdvetmanual.com/). MSD Veterinary Manual.
- [American Veterinary Medical Association Practice Resources](https://www.avma.org/resources-tools). American Veterinary Medical Association.

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> This article is educational professional reference material for veterinary audiences. It is not a substitute for veterinary diagnosis, individual clinical judgment, current product labeling, or applicable regulatory requirements.