What is Dr. Zubair Khalid's research focus?

Dr. Zubair Khalid specializes in molecular virology, mRNA vaccine development, and computational biology, with a focus on avian pathogens like IBDV and Avian Reovirus.

Where is Dr. Zubair Khalid currently working?

Dr. Zubair Khalid is a Postdoctoral Research Associate at the University of Maryland (UMD), specifically within the Department of Animal and Avian Sciences.

Cat Heart Murmur: Causes and Next Steps

Name: Cat Heart Murmur: Causes and Next Steps
Creator: Dr. Zubair Khalid

By Dr. Zubair Khalid, DVM, MS, PhD · 2026-09-20

A cat heart murmur is an abnormal sound your veterinarian hears through a stethoscope between the normal "lub" and "dub" heart sounds. It means blood is flowing in a way that creates turbulence, and in cats the single most important cause to rule out is hypertrophic cardiomyopathy (HCM), the most common heart disease in the species [1].

The reassuring news is that many murmurs in cats are harmless, dynamic, or stress-related. The challenging news is that a murmur's loudness tells you almost nothing about how sick the heart is. Some cats with severe HCM have no murmur at all, and some cats with a loud murmur have a completely normal heart [1][2]. That mismatch is why the murmur itself is a starting point, not an answer.

What a Heart Murmur Actually Is

Blood moving smoothly through the heart is silent. When it hits a rough surface, squeezes through a narrowed opening, or swirls backward through a leaky valve, it becomes turbulent and audible. That turbulence is the murmur.

Veterinarians describe murmurs by timing (systolic, diastolic, or continuous), by the point on the chest where they are loudest, and by grade. A systolic murmur, heard during the heart's contraction phase, is by far the most common type in cats. A continuous murmur, heard throughout the whole cycle, raises suspicion for a specific congenital defect called patent ductus arteriosus.

One feline-specific wrinkle matters a great deal. Cats have a dynamic outflow tract, meaning the speed of blood leaving the left ventricle can change from minute to minute based on heart rate, stress, and hydration. This is why a cat murmur can appear during one exam and vanish at the next. It is also why a murmur can be provoked by pressing the stethoscope firmly against the chest wall, a phenomenon documented in apparently healthy cats [3].

The Murmur Grading Scale (I to VI)

Grading is a subjective but standardized way to describe how loud a murmur is. The scale runs from I to VI.

Grade	What the veterinarian hears
I	Very soft, heard only with concentrated effort
II	Soft, but clearly audible immediately
III	Moderate intensity, easy to hear
IV	Loud, but no thrill felt through the chest wall
V	Very loud, with a palpable thrill
VI	Loudest possible, audible with the stethoscope barely touching the chest

A "thrill" is a vibration you can feel with your fingertips over the chest, like the buzz of a cell phone. Its presence separates grade IV from grade V.

The critical teaching point for owners is this: grade does not equal severity. A grade II murmur can sit on top of advanced HCM, and a grade IV murmur can sit on top of a structurally normal heart. Studies of cats with HCM have repeatedly shown that the absence of a murmur is itself a marker of worse outcome, because those cats tend to present later with more advanced disease [2]. Atenolol, a beta-blocker used in some cats with subclinical HCM, has been shown to reduce murmur grade from a median of 3/6 to 2/6, but that change reflects altered blood flow dynamics rather than a cure [4].

How Common Are Murmurs in Cats?

Murmurs are common in the general cat population. In one prospective study of 103 overtly healthy cats, 22 (21%) had a detectable heart murmur [5]. When echocardiography was performed on seven of those cats, one had a completely normal heart, while six had abnormalities including hypertrophic cardiomyopathy and left ventricular concentric hypertrophy with valvular disease [5].

A separate study found that iatrogenic murmurs, meaning murmurs caused by the examination itself rather than by disease, occurred in 28.2% of apparently healthy cats during a provocative maneuver [3]. Those murmurs were more likely in older cats and in cats with lower body condition scores.

The takeaway is that a murmur is a common finding that deserves investigation, not a rare finding that guarantees disease.

Causes of Heart Murmurs in Cats

The table below summarizes the major categories, what typically causes them, and the cats most likely to be affected.

Cause	Typical signalment	Key features
Hypertrophic cardiomyopathy (HCM)	Any age from 3 months up, any breed, any sex. Higher prevalence reported in male and domestic shorthair cats [1]	Most common feline cardiomyopathy. May or may not produce a murmur or gallop sound. Severe cases can lead to heart failure or arterial thromboembolism [1]
Valvular disease	Older cats	Leaky or thickened valves create turbulence. Often found alongside other cardiac changes
Congenital heart disease	Young cats, often under 1 year	Ventricular septal defects are the most common feline congenital defect, followed closely by aortic stenosis and hypertrophic obstructive cardiomyopathy [6]. Overall prevalence in mixed-breed cats is low, around 0.14% [6]
Anemia	Any cat with significant blood loss or hemolysis	Thin blood flows faster and more turbulently. A functional murmur that resolves when the anemia is treated
Hyperthyroidism	Middle-aged to older cats	High thyroid hormone drives a hyperdynamic circulation. Also a recognized cause of mild to moderate left ventricular wall thickening that must be ruled out before diagnosing HCM [1]
Systemic hypertension	Older cats, often with kidney disease or hyperthyroidism	High afterload changes flow dynamics and can cause murmur plus other organ damage
Functional or dynamic murmurs	Any cat, especially under stress	No structural disease. Common, often intermittent, and frequently provoked by examination [3]

Hypertrophic Cardiomyopathy: The Main Concern

HCM is defined by thickening of the left ventricular wall that is not explained by another condition. It affects up to approximately 15% of the domestic cat population, mostly as subclinical disease [1]. Cats of any age from 3 months upward, of either sex and any breed, can be affected, with a reported higher prevalence in males and domestic shorthairs [1].

The disease is heterogeneous. The thickening can be concentrated in the interventricular septum, the free wall, the apex, or the midventricle. A recent report described the first documented case of apical HCM in a cat, in a 4-year-old Sphynx evaluated for a heart murmur [7]. Another report described midventricular obstruction in eight cats, all of which had left ventricular hypertrophy at the level of the papillary muscles [8].

HCM can also be dynamic in a different sense. Systolic anterior motion of the mitral valve (SAM) is the most common cause of dynamic left ventricular outflow tract obstruction in cats with HCM [1]. When the mitral valve leaflet gets pulled into the outflow tract during systole, it both obstructs flow and worsens mitral regurgitation. This is the mechanism behind hypertrophic obstructive cardiomyopathy, and it can be severe enough to generate a loud murmur and a high outflow velocity [9].

A particularly important point for owners: HCM with mild to moderate wall thickening is a diagnosis of exclusion [1]. There is no single definitive test for those cats. Other conditions that can cause mild to moderate left ventricular thickening, including hyperthyroidism, systemic hypertension, acromegaly, and dehydration, must be ruled out first [1].

Other Cardiomyopathies and Structural Disease

Beyond HCM, cats can develop restrictive or unclassified cardiomyopathies, arrhythmogenic right ventricular cardiomyopathy, and non-cardiomyopathic forms of heart disease [10]. Valvular disease in cats is less common than in dogs but does occur, particularly in older cats, and often coexists with other findings.

Congenital defects are uncommon but important because some are correctable. Ventricular septal defects lead the list in cats, followed closely by aortic stenosis and hypertrophic obstructive cardiomyopathy [6]. These are typically identified in young cats during their first examinations.

Non-Cardiac Causes

Anemia, hyperthyroidism, and systemic hypertension all change blood flow in ways that can produce a murmur without primary structural heart disease. Hyperthyroidism deserves special emphasis because it both causes murmurs and mimics HCM on echocardiography [1]. Any older cat with a new murmur should have thyroid testing.

Why Murmur Intensity Does Not Predict Severity

This is the concept that trips up owners most often. A loud murmur means turbulent flow. It does not mean a large amount of damage.

Consider two cats. Cat A has a small ventricular septal defect. Blood shoots through a narrow hole at high velocity, creating a very loud murmur, but the heart is otherwise coping well. Cat B has advanced HCM with a stiff, thick ventricle and a massively enlarged left atrium. Blood may be moving slowly and smoothly, producing no murmur at all, yet this cat is at high risk for heart failure and arterial thromboembolism.

The data support this. In a study of 282 cats with HCM, the absence of a murmur was a univariable predictor of increased risk of cardiac death [2]. In other words, the quiet cats did worse. A murmur is a clue about flow, not a score of disease burden.

What Your Veterinarian Should Do Next

When a murmur is detected, the evaluation follows a logical sequence. The goal is to answer three questions: Is there structural heart disease? Is it causing hemodynamic consequences? Is the cat at risk for heart failure or thromboembolism?

Step 1: Full Cardiac Auscultation

A complete auscultation means listening over all four valve areas on both sides of the chest, not just where the murmur is loudest. The veterinarian is listening for:

The murmur's timing, grade, and point of maximal intensity
A gallop sound, which is an extra diastolic sound and a marker of worse prognosis in HCM [2]
An arrhythmia, which may indicate conduction disease or arrhythmogenic cardiomyopathy
Lung sounds, to check for crackles or muffled sounds that suggest fluid

A gallop sound and an arrhythmia are both independent predictors of increased cardiac death risk in cats with HCM [2]. Their presence changes the urgency of the workup.

Step 2: Blood Pressure Measurement

Systemic hypertension can cause or worsen murmurs and can also cause left ventricular thickening that mimics HCM [1]. Doppler systolic blood pressure measurement is standard. Cats with a systolic pressure above 170 mmHg are typically excluded from HCM study populations because hypertension itself can produce the echocardiographic changes [8]. Blood pressure must be measured before or alongside echocardiography.

Step 3: Blood Tests

A minimum database includes a complete blood count to rule out anemia, a chemistry panel, and a thyroid panel in any cat old enough to develop hyperthyroidism. These tests address the reversible causes of murmurs and of left ventricular thickening.

Cardiac biomarkers are useful adjuncts. A point-of-care NT-proBNP ELISA differentiated cats with moderate to severe occult heart disease with a sensitivity of 83.8% and specificity of 82.6%, and a positive result increased the likelihood of moderate or severe disease by a factor of 4.8 [10]. In a cat with hypertrophic obstructive cardiomyopathy, NT-proBNP exceeded 1,500 pmol/L at diagnosis and fell to 870 pmol/L after treatment [9].

The critical caveat: biomarkers should not be relied on solely to diagnose HCM [1]. A normal NT-proBNP does not rule out mild disease, and an elevated result does not tell you which disease the cat has.

Step 4: Echocardiography

Echocardiography is the definitive test. It shows wall thickness, chamber size, valve motion, and flow velocities. It is the only way to distinguish HCM from valvular disease, congenital defects, and the reversible thickening caused by hyperthyroidism or hypertension.

Echocardiography is also how risk is stratified. Left atrial enlargement, decreased left atrial function, spontaneous echo contrast, and thrombus are all associated with decreased survival in cats with HCM [2]. Left atrial size and heart sound were the two most significant predictors of HCM likelihood in a retrospective study of 354 cats [11].

When echocardiography is not immediately available, thoracic radiography can help. Substantial left atrial enlargement can often be identified radiographically in cats with severe HCM [1]. Radiography alone has limited accuracy for diagnosing HCM, but it remains useful for assessing heart size and for detecting pulmonary edema or pleural effusion when heart failure is suspected.

flowchart TD
    [Murmur detected] --> [Full cardiac auscultation]
    [Full cardiac auscultation] --> [Measure blood pressure]
    [Measure blood pressure] --> [Blood tests and thyroid panel]
    [Blood tests and thyroid panel] --> [Cardiac biomarker]
    [Cardiac biomarker] --> {Echocardiography available}
    {Echocardiography available} --> [Echocardiography]
    {Echocardiography available} --> [Thoracic radiographs]
    [Echocardiography] --> [Stage disease and risk]
    [Thoracic radiographs] --> [Stage disease and risk]
    [Stage disease and risk] --> [Plan monitoring]
    [Stage disease and risk] --> [Consider treatment]

When to Recommend Echocardiography

Echocardiography is the gold standard for the final diagnosis of cardiac disease in cats [11]. It should be recommended in the following situations:

Any new murmur in a cat, particularly if a gallop sound or arrhythmia is also present
A murmur in a young cat, to screen for congenital defects
A murmur in a breeding cat, because HCM screening is a core part of responsible breeding programs [12]
A cat with a murmur plus clinical signs such as lethargy, exercise intolerance, or difficulty breathing
A cat with an elevated NT-proBNP or troponin result
A cat with a murmur and radiographic cardiomegaly
A cat with a murmur and a known predisposing condition such as hyperthyroidism or hypertension, once those are controlled
Follow-up for a cat with known HCM, to track progression

Screening for HCM is particularly challenging because mild disease can be difficult to differentiate from a normal phenotype [12]. This is why serial examinations over time are often more informative than a single study.

Treatment: What Happens if HCM Is Diagnosed

Treatment depends on stage. A cat with subclinical HCM and no left atrial enlargement may need no medication at all, just monitoring. A cat with outflow obstruction may benefit from a beta-blocker. Atenolol decreased heart rate, reduced murmur grade, and reduced left ventricular outflow tract velocity in cats with subclinical HCM [4]. In a cat with hypertrophic obstructive cardiomyopathy, carvedilol combined with disopyramide reduced outflow velocity and NT-proBNP and eliminated systolic anterior motion of the mitral valve over 141 days [9].

Cats that develop congestive heart failure need diuretics and additional support. Pimobendan has been studied in cats with subclinical HCM. A single dose increased tissue Doppler peak systolic velocity of the mitral annulus but did not significantly change heart rate, blood pressure, murmur grade, left atrial size, or left ventricular fractional shortening [13]. Its role in subclinical disease remains an area of active investigation.

Cats with severe HCM and left atrial enlargement are at risk for arterial thromboembolism, a devastating complication in which a clot lodges in a limb or, rarely, elsewhere. A case report described lingual artery thromboembolism in a cat with HCM, causing tongue infarction [14]. Platelet activation is increased in cats with severe HCM, and increased P-selectin expression correlates with the presence of a heart murmur [15]. Antithrombotic therapy is typically considered in cats with significant left atrial enlargement or spontaneous echo contrast.

Counseling Owners on Home Monitoring

The single most valuable thing an owner can do at home is count the sleeping respiratory rate.

How to Count the Sleeping Respiratory Rate

Wait until your cat is asleep, not just resting.
Watch the chest wall rise and fall.
Count each rise-and-fall as one breath.
Count for a full 30 seconds and multiply by two, or count for a full 60 seconds.
Record the number with the date and time.
Do this at roughly the same time each day, ideally when the cat is naturally asleep.

A normal sleeping respiratory rate in a healthy cat is generally under 30 breaths per minute. A rate that is consistently above 30, or that is trending upward over several days, warrants a call to your veterinarian. This is often the earliest sign that heart failure is developing, before the cat shows obvious distress.

Other Signs to Watch For

Open-mouth breathing or panting at rest
Increased effort to breathe, with visible abdominal movement
Hiding more than usual or withdrawing from family activity
Reduced appetite or weight loss
Sudden weakness, paralysis, or vocalization, which may indicate thromboembolism
Collapse or fainting

Any of these signs warrants immediate veterinary attention.

What Is Still Uncertain

Feline HCM research is active, and several questions remain open. The genetic cause of HCM has been identified in two breeds and is suspected in another, but for most cats the cause is unknown [1]. The optimal timing of echocardiographic screening in at-risk cats is not fully settled, and mild disease remains difficult to distinguish from normal variation [12]. The role of pimobendan in subclinical HCM is still being investigated [13]. Long-term studies are needed to determine whether treating subclinical HCM changes outcomes such as sudden cardiac death [4].

Limitations and When to Contact a Veterinarian

This article is educational and is not a substitute for veterinary diagnosis or treatment. Individual cats vary, and a murmur that is benign in one cat may signal serious disease in another.

Contact a veterinarian promptly if your cat has any of the following:

A newly detected murmur, especially with a gallop sound or arrhythmia
A sleeping respiratory rate consistently above 30 breaths per minute
Open-mouth breathing, panting at rest, or increased breathing effort
Sudden hind limb weakness, paralysis, cold limbs, or vocalization
Collapse, fainting, or unexplained lethargy
Reduced appetite, weight loss, or hiding behavior
Known HCM with new or worsening clinical signs

If your cat is already under treatment for heart disease and develops any of these signs, call your veterinarian or an emergency clinic immediately rather than waiting for the next scheduled recheck.

Frequently Asked Questions

Does a heart murmur in cats always mean heart disease?

No. Many murmurs in cats are functional, dynamic, or stress-related, and some cats with murmurs have structurally normal hearts. In one study of healthy cats with murmurs, one of seven examined by echocardiography had a completely normal heart [5].

Is a louder murmur more dangerous?

No. Murmur grade reflects turbulence, not disease severity. Cats with severe HCM can have no murmur at all, and the absence of a murmur has been associated with increased risk of cardiac death in some studies [2].

What is the most common cause of a heart murmur in cats?

Hypertrophic cardiomyopathy is the most common form of feline cardiomyopathy and a leading concern when a murmur is found [1]. Other causes include valvular disease, congenital defects, anemia, hyperthyroidism, and systemic hypertension.

Can a cat heart murmur go away on its own?

Yes, some do. Dynamic murmurs related to stress, heart rate, or examination technique can disappear between visits. Iatrogenic murmurs provoked by stethoscope pressure were found in 28.2% of apparently healthy cats [3]. A murmur that resolves does not always mean the underlying heart is normal, so follow-up matters.

What tests does a cat with a murmur need?

A full cardiac auscultation, blood pressure measurement, blood tests including a thyroid panel, and often a cardiac biomarker such as NT-proBNP. Echocardiography is the definitive test and is the gold standard for diagnosis [11].

Can HCM be diagnosed without an echocardiogram?

Mild to moderate HCM cannot be reliably diagnosed without echocardiography because it is a diagnosis of exclusion [1]. Radiography can show substantial left atrial enlargement in severe cases, but it is not a substitute for ultrasound.

Should I breed a cat that has a heart murmur?

No. HCM screening is a standard part of responsible breeding, and cats with murmurs are typically screened before breeding decisions are made [12]. Discuss the specific situation with a veterinarian experienced in feline cardiac screening.

How often should a cat with a murmur be rechecked?

The interval depends on the diagnosis. Cats with subclinical HCM are often rechecked every 6 to 12 months, while cats with more advanced disease may need more frequent monitoring. Your veterinarian will set the schedule based on echocardiographic findings and clinical signs.