Hypertrophic Cardiomyopathy in Cats

Hypertrophic cardiomyopathy (HCM) is the most common cardiac disease in cats, affecting approximately 10–15% of the general feline population. [2, 5] This condition is characterized by thickening of the left ventricular wall, which impairs the heart’s ability to relax and fill properly. While many cats with HCM remain asymptomatic for years, others may develop life-threatening complications such as congestive heart failure (CHF) or arterial thromboembolism (ATE). This article provides a comprehensive, evidence-based review of feline HCM, covering causes, diagnosis, treatment, and home care, with a focus on helping owners recognize red-flag signs and understand when to seek veterinary attention.

Quick Q&A

Question: What is hypertrophic cardiomyopathy in cats? Answer: Hypertrophic cardiomyopathy (HCM) is a disease where the heart muscle becomes abnormally thick, reducing the heart’s ability to relax and fill with blood. It is the most common heart disease in cats and can lead to heart failure, blood clots, and sudden death. Early detection through regular veterinary check-ups and echocardiography is key to managing the condition.

What is Hypertrophic Cardiomyopathy (HCM) in Cats?

HCM is a primary myocardial disorder that results in concentric hypertrophy (thickening) of the left ventricular free wall and/or interventricular septum. [30] Unlike dilated cardiomyopathy, which involves a thin, weak heart muscle, the thickened walls in HCM become stiff and non-compliant, leading to diastolic dysfunction. [29] This means the heart cannot relax adequately to fill with blood during diastole, causing increased pressure in the left atrium and pulmonary veins. Over time, this can lead to left atrial enlargement, pulmonary congestion, and eventually CHF. [6]

The condition is also a major cause of cardiogenic arterial thromboembolism (CATE), where a blood clot dislodges from the left atrium and blocks blood flow to vital organs, most commonly the hindlimbs (saddle thrombus). [10, 17] Less common sites include the renal arteries, brain, and even the lingual artery, as reported in a recent case. [10]

Causes and Risk Factors

Genetic Basis

A strong genetic component has been identified in certain breeds. In Maine Coon cats, a mutation in the MYBPC3 gene is associated with HCM. In Sphynx and British Shorthair cats, a variant in the ALMS1 gene (p.G2462R) has been studied, but recent evidence from Thailand suggests this variant may not play a primary role in all populations. [4] The prevalence of HCM is highest in Persian, Sphynx, and British Shorthair cats, but mixed-breed cats are also commonly affected. [17]

Other Risk Factors

• Age: Adult cats (median 4–7 years) are most commonly diagnosed, though HCM can occur in young cats. [5, 17]
• Sex: Male cats are overrepresented, with clinical studies reporting 60–75% male predominance. [5, 17]
• Body Condition: Obesity (body condition score ≥6/9) is an independent risk factor for HCM. [24]
• Concurrent Diseases: Hyperthyroidism can cause a reversible hypertrophic phenotype (HCMP) that mimics HCM. [20, 31] Hypersomatotropism (acromegaly) is also associated with HCM in cats without diabetes mellitus. [22]

Transient Myocardial Thickening (TMT)

It is important to distinguish HCM from transient myocardial thickening, a reversible condition triggered by acute stress, systemic illness, or toxins (e.g., minoxidil, paracetamol). [7, 34, 39, 40] TMT can present with severe left ventricular hypertrophy and even CHF, but wall thickness normalizes within weeks to months. Differentiation is critical because TMT carries a much better prognosis and does not require lifelong therapy. [34]

Clinical Signs and Red Flags

Many cats with HCM are asymptomatic for years. When signs do appear, they are often subtle and progressive. The most common presentations include:

• Respiratory signs: Tachypnea (rapid breathing), dyspnea (difficulty breathing), open-mouth breathing, or coughing (uncommon in cats). These often indicate pulmonary edema or pleural effusion due to CHF.
• Lethargy and anorexia: Reduced activity and appetite.
• Syncope or collapse: Fainting episodes due to arrhythmias or outflow tract obstruction.
• Acute hindlimb paralysis: Sudden onset of pain, cold extremities, and inability to walk – classic for ATE (saddle thrombus). [3, 17]
• Unexplained vocalization or hiding: Signs of pain or distress.

Red-Flag Signs Warranting Immediate Veterinary Visit

• Rapid or labored breathing (resting respiratory rate >30 breaths per minute)
• Sudden hindlimb weakness or paralysis
• Collapse or fainting
• Blue or pale gums (cyanosis)
• Refusal to eat for more than 12 hours
• Any acute change in behavior (e.g., hiding, crying, aggression)

If you notice any of these signs, seek emergency veterinary care immediately. Delay can be fatal.

Diagnosis

Definitive diagnosis of HCM requires echocardiography. The American College of Veterinary Internal Medicine (ACVIM) consensus guidelines recommend echocardiographic measurement of left ventricular wall thickness >6 mm at end-diastole to diagnose HCM. [12, 21] However, measurement methods vary between 2D and M-mode and between different imaging views, and these are not interchangeable. [12, 21] Standardization is essential for accurate diagnosis and staging.

Additional Diagnostic Tests

• Electrocardiography (ECG): ECG has limited sensitivity for screening subclinical HCM. A 6-lead ECG, even with advanced parameters like ST-segment elevation, cannot reliably replace echocardiography. [23]
• Cardiac Biomarkers: N-terminal pro-B-type natriuretic peptide (NT-proBNP) and high-sensitivity cardiac troponin I (cTnI) can support the diagnosis. [14, 24] NT-proBNP ≥109 pmol/L was independently associated with cardiac disease in cats with asymptomatic murmurs. [24] cTnI levels are significantly higher in cats with HCM compared to healthy controls and correlate with disease severity. [14, 19]
• Thoracic Radiography: Useful for detecting left atrial enlargement, pulmonary edema, or pleural effusion, but not sensitive for early HCM.
• Blood Pressure Measurement: To rule out systemic hypertension as a cause of left ventricular hypertrophy. [20]

Staging (ACVIM Classification)

• Stage B1: Asymptomatic, no left atrial enlargement (LA:Ao <1.6).
• Stage B2: Asymptomatic with left atrial enlargement (LA:Ao ≥1.6).
• Stage C: Clinical signs of CHF (present or past).
• Stage D: Refractory CHF.

Approximately 60% of asymptomatic cats with murmurs have cardiac disease, with HCM being the most common. [24] The majority of cats diagnosed with HCM on echocardiography are in stage B1, and many remain stable for years. [1]

Treatment and Management

Treatment goals include controlling signs of CHF, preventing thromboembolism, and slowing disease progression. There is no cure for HCM, but early intervention can improve quality of life and survival.

Pharmacological Therapy

• Diuretics (Furosemide): First-line for CHF. Doses are titrated to the lowest effective level to avoid dehydration.
• Pimobendan: A positive inotrope and vasodilator (phosphodiesterase III inhibitor). It improves systolic and diastolic function and reduces left atrial size. [33] Pimobendan is recommended for cats with CHF (stage C/D) and may be considered for stage B2 with severe left atrial enlargement. It is contraindicated in cats with fixed outflow tract obstruction.
• Beta-Blockers (Atenolol, Carvedilol): Used to reduce heart rate, improve filling, and relieve left ventricular outflow tract obstruction (LVOTO). High-dose carvedilol has been shown to reduce LVOT velocity and improve myocardial function in cats with obstructive HCM. [19]
• Disopyramide: A class Ia antiarrhythmic that can be added to carvedilol for refractory LVOTO, with significant reduction in cardiac troponin I levels. [38]
• Antithrombotics (Clopidogrel, Aspirin): Clopidogrel is the preferred antiplatelet agent for preventing ATE. Low-dose delayed-release rapamycin (LDDRR) is an emerging therapy that reduces platelet activation and procoagulant phenotypes. [11]
• SGLT2 Inhibitors (Bexagliflozin): In cats with CHF and advanced chronic kidney disease, SGLT2 inhibitors may serve as an adjunct decongestive strategy, but careful monitoring for ketoacidosis is required. [15]
• Calcium Channel Blockers (Diltiazem): Less commonly used today due to the availability of pimobendan and beta-blockers. Amlodipine is primarily used for hypertension, not HCM.

Emerging Therapies

• mTOR Inhibitors: In silico studies have identified dihydro-alpha-ergocryptine as a potential feline-specific mTOR inhibitor, but clinical trials are lacking. [2]
• Proteomics and Biomarkers: SWATH-MS plasma proteomics has identified dysregulated pathways (complement, coagulation, lipid metabolism) that may lead to novel therapeutic targets. [18]

Surgical and Interventional Options

• Subcutaneous Ureteral Bypass (SUB): For cats with concurrent ureteral obstruction and mild HCM, SUB placement is not contraindicated, as mild cardiomyopathy did not affect outcomes in one study. [1]
• Peritoneal Dialysis: Can be life-saving for anuric acute kidney injury secondary to ATE when hemodialysis is unavailable. [3]

Home Care and Monitoring

Owners play a crucial role in managing HCM. Key recommendations include:

• Resting Respiratory Rate (RRR): Monitor RRR at home (normal <30 breaths/min). An increase of >30% from baseline may indicate early CHF.
• Weight Monitoring: Weekly weighing to detect fluid retention.
• Diet: Low-sodium diets are recommended, especially for cats with CHF. Avoid high-salt treats.
• Stress Reduction: Minimize environmental stress, as stress can trigger CHF or ATE.
• Medication Compliance: Use pill pockets, compound pharmacies, or transdermal formulations to ease administration.
• Regular Veterinary Check-ups: Echocardiography every 6–12 months for stage B1/B2, more frequently for stage C/D.

Prognosis

The prognosis is variable. Cats with mild, non-obstructive HCM and normal left atrial size (stage B1) often live many years. [1] Once CHF develops, median survival time is approximately 6–18 months despite therapy. [17] The presence of ATE carries a grave prognosis, with only 8% survival in one Iranian study. [17] However, a cat with lingual artery thromboembolism was euthanized due to poor outcome, highlighting the severity of thromboembolic events. [10]

The platelet:neutrophil ratio (PNR) is a novel, cost-effective biomarker: cats with PNR <40 at diagnosis have a significantly higher risk of cardiac-related mortality. [37]

FAQ

How is hypertrophic cardiomyopathy inherited in cats?

HCM has a strong genetic component, especially in Maine Coon (MYBPC3 mutation) and Sphynx (ALMS1 variant) breeds. However, the ALMS1 variant may not be predictive in all populations. [4] Most cases in mixed-breed cats are likely polygenic or due to spontaneous mutations.

Can stress cause hypertrophic cardiomyopathy in cats?

Stress alone does not cause HCM, but it can trigger acute decompensation, such as pulmonary edema or ATE, in cats with pre-existing disease. Stress also contributes to transient myocardial thickening (TMT) in some cats. [7, 39]

What are the signs of a blood clot in a cat with HCM?

The classic sign is sudden hindlimb paralysis (saddle thrombus). Cats may cry out, drag one or both hindlimbs, and have cold, pale paw pads. Less common presentations include acute blindness (cerebral thromboembolism) or tongue infarction (lingual artery thromboembolism). [10, 17]

Is there a cure for feline hypertrophic cardiomyopathy?

No, there is no cure. However, many cats respond well to medical management and can enjoy a good quality of life for years. The goal is to manage symptoms, prevent complications, and slow disease progression.

Can a cat with HCM live a normal life?

Yes, many cats with subclinical HCM (stage B1) live normal lifespans. Regular monitoring and lifestyle adjustments (low-stress, low-sodium diet) are important. Cats with CHF require more intensive management and have a guarded prognosis.

How often should a cat with HCM see a cardiologist?

For asymptomatic cats, annual echocardiography is recommended. For cats with CHF or significant left atrial enlargement, more frequent evaluation (every 3–6 months) is warranted.

References

[1] Cassou C, Plante C, Vachon C, et al. Characterization and outcomes of cats with cardiomyopathy undergoing subcutaneous ureteral bypass device placement. J Vet Intern Med. 2026. [PMID: 42384842]

[2] Gao J, Li M, Xiang R, et al. In Silico Discovery of mTOR Inhibitors as Potential Therapeutics for Feline Hypertrophic Cardiomyopathy. J Mol Model. 2026. [PMID: 42371166]

[3] Umeda N, Nakazawa K. Successful management of anuric acute kidney injury associated with aortic thromboembolism with peritoneal dialysis in a cat. JFMS Open Rep. 2026. [PMID: 42369665]

[4] Sussadee M, Jarudecha T, Muikaew R, et al. Prevalence and Clinical Relevance of Alström Syndrome Protein 1 Gene Variant and Feline Hypertrophic Cardiomyopathy in Sphynx Cats in Thailand. Animals (Basel). 2026. [PMID: 42353426]

[5] El Atmani H, Kichou F, Tarducci A, et al. First Description of Hypertrophic Cardiomyopathy Phenotype in Apparently Healthy Cats in Morocco: An Echocardiographic Prevalence Study. Animals (Basel). 2026. [PMID: 42353413]

[6] Varlik T, Algan D, Tanaka R, et al. Left Atrioventricular Coupling Index in Feline Hypertrophic Cardiomyopathy: Association with Disease Severity and Arterial Thromboembolism. Vet Sci. 2026. [PMID: 42188963]

[7] Park SW, Kim K, Lee JW, et al. Presumed acute myocardial damage in a British Shorthair cat with previously diagnosed hypertrophic cardiomyopathy. Ir Vet J. 2026. [PMID: 42174688]

[8] Wood JE, Ames MK, Kaplan JL, et al. Characterization of the myocardial and renal renin-angiotensin system in normal cats and cats with hypertrophic cardiomyopathy. J Vet Intern Med. 2026. [PMID: 42105302]

[9] Nijveldt E, Yildiz V, Schober KE. Echocardiographic evaluation of aortic root size in cats with hypertrophic cardiomyopathy. J Vet Med Sci. 2026. [PMID: 42036317]

[10] Blunschi F, Riwers J, Jaresova T, et al. Tongue infarction in suspected lingual artery thromboembolism in a cat with hypertrophic cardiomyopathy. JFMS Open Rep. 2026. [PMID: 41978704]

[11] Shaverdian M, Nguyen N, Fitzgerald S, et al. Ex vivo effects of low dose delayed release rapamycin on agonist-induced platelet aggregation, activation and procoagulant platelet phenotypes in domestic cats. Sci Rep. 2026. [PMID: 41965408]

[12] Grosso G, Schober KE. Effect of echocardiographic imaging view and methods on left ventricular wall-thickness measurements in normal cats and cats with hypertrophic cardiomyopathy. J Vet Intern Med. 2026. [PMID: 41964609]

[13] Ma D, Sutthiprapa W, Xu X, et al. Microlancet-assisted internal urethrotomy with stent placement for feline pelvic urethral stricture: a case report. Front Vet Sci. 2026. [PMID: 41960354]

[14] Lidbury JA, Meyers RC, Saunders AB, et al. Analytical validation and clinical evaluation of a high-sensitivity cardiac troponin I immunoassay for use in cats. PLoS One. 2026. [PMID: 41950232]

[15] Kim BJ, Song KH. Case Report: Bexagliflozin as an adjunct decongestive strategy in a cat with congestive heart failure and advanced chronic kidney disease. Front Vet Sci. 2026. [PMID: 41908952]

[16] Jeong CR, Shin YJ, Park C. Comparative Study of Speckle Tracking Echocardiography in Normal and Hypertrophic Cardiomyopathy Cats. Vet Sci. 2026. [PMID: 41893695]

[17] Jalilian M, Pahlevaninezhad N, Yazdanjoo Z, et al. Hypertrophic cardiomyopathy in cats: clinical prevalence, risk factors, and outcomes of arterial thromboembolism in a referral population in Tehran, Iran (2020-2024). BMC Vet Res. 2026. [PMID: 41888795]

[18] Ravuri HG, Daniels AL, Sadowski P, et al. Understanding Pathophysiological Complexity of Feline Hypertrophic Cardiomyopathy Using SWATH-MS Plasma Proteomics. Animals (Basel). 2026. [PMID: 41828989]

[19] Satomi S, Suzuki R, Yuchi Y, et al. Efficacy of high-dose carvedilol treatment for cats with stage B1 obstructive hypertrophic cardiomyopathy. J Feline Med Surg. 2026. [PMID: 41792123]

[20] Foulex P, Reslinger B, Kurtz M, et al. Hypertrophic cardiomyopathy is not the sole echocardiographic phenotype associated with hyperthyroidism in cats: a retrospective study in 147 cats (2005-2025). J Vet Intern Med. 2026. [PMID: 41742580]

[21] Novo Matos J, Luis Fuentes V. Left ventricular wall thickness in cats: agreement between echocardiographic views. J Vet Intern Med. 2026. [PMID: 41742568]

[22] Miceli D, Niessen SJM, Rey Amunategui JP, et al. Hypersomatotropism without concurrent diabetes mellitus in cats: 28 cases (2014-2024). J Vet Intern Med. 2026. [PMID: 41742520]

[23] Gardner L, Partington C, Novo Matos J. Accuracy of 6-lead electrocardiography in identifying subclinical hypertrophic cardiomyopathy in cats. J Vet Intern Med. 2026. [PMID: 41742508]

[24] Carter R, Partington C, Novo Matos J. Accuracy of combined signalment, physical examination and cardiac biomarkers in screening cats with asymptomatic murmurs for cardiac disease. J Vet Intern Med. 2026. [PMID: 41742490]

[25] Tohthong P, Tosuwan J, Surachetpong SD. Left atrial stiffness as a novel echocardiographic parameter of atrial dysfunction in cats with hypertrophic cardiomyopathy: A two-dimensional speckle-tracking study. Vet World. 2025. [PMID: 41716159]

[26] Matsuura T, Morita S, Fukushima R. Systemic gene expression mapping of voltage-gated calcium channel α1-subunits in cats. Open Vet J. 2025. [PMID: 41630730]

[27] Constantin I, Pop R, Negoescu A, et al. Glyco-Architectural Remodelling of the Feline Heart: Age- and HCM-Related Insights from Lectin Histochemistry. Life (Basel). 2025. [PMID: 41598176]

[28] Li RHL, Shaverdian M, Chen C, et al. Functional toll-like receptor 4 links endotoxin sensing to platelet priming in feline platelets. Front Vet Sci. 2025. [PMID: 41574253]

[29] Naseri A, Ider M, Sahin HB, et al. Clinical value of the tissue Doppler derived index of myocardial performance (Tei index) in cats with hypertrophic cardiomyopathy. J Vet Cardiol. 2026. [PMID: 41499857]

[30] de Sousa FG, Muzzi RAL, de Araújo RB, et al. Linking clinical and imaging diagnostic assessments of the feline hypertrophic cardiomyopathy phenotype. Front Vet Sci. 2025. [PMID: 41487485]

[31] van Zuiden B, Santarelli G, Galac S, et al. Cardiac Abnormalities in Feline Hyperthyroidism. Vet Sci. 2025. [PMID: 41472095]

[32] Jordan H, Fox PR, Schober KE. Echocardiographic diagnosis of hypertrophic cardiomyopathy confined to the left ventricular apex in a cat. JFMS Open Rep. 2025. [PMID: 41394092]

[33] Gordon SG, Saunders AB, Wesselowski S, et al. Use of pimobendan in cats: a practical evidence-based review. J Feline Med Surg. 2025. [PMID: 41384556]

[34] Park SW, Kim K, Lee YJ, et al. Prevalence and characteristics of transient myocardial thickening in cats with hypertrophic cardiomyopathy phenotypes. Vet Q. 2025. [PMID: 41358391]

[35] Qu LY, Quan FS, Shi SM, et al. CRISPR/Cas9-mediated CH2 deletion of Fel d1 triggers transcriptomic reprogramming and disease-associated pathways in feline cells. Front Cell Dev Biol. 2025. [PMID: 41358006]

[36] Granger KL Jr, Gross C, Frank C, et al. Multisystemic manifestations of highly pathogenic avian influenza (H5N1) in a young domestic shorthair cat. JFMS Open Rep. 2025. [PMID: 41244636]

[37] Yoon LI, Li RH. Evaluation of neutrophil:lymphocyte and platelet:neutrophil ratios and their prognostic utility in cats with hypertrophic cardiomyopathy and cardiogenic arterial thromboembolism. J Feline Med Surg. 2025. [PMID: 41165112]

[38] Satomi S, Suzuki R, Yuchi Y, et al. Disopyramide Therapy in Cats with Obstructive Hypertrophic Cardiomyopathy Non-Responsive to Carvedilol. Vet Sci. 2025. [PMID: 41150139]

[39] Park SW, Kim K, Lee YJ, et al. Congestive heart failure after enterotomy in a cat with asymptomatic transient myocardial thickening. Ir Vet J. 2025. [PMID: 41137073]

[40] Ferri C, Dossin O, Gouni V. Heart failure associated with minoxidil intoxication in a cat. J Vet Cardiol. 2025. [PMID: 41046802]