Hypertrophic cardiomyopathy (HCM) is the most common heart disease in cats — the heart muscle thickens, the chambers fill less efficiently, and many cats look normal for years before suddenly showing rapid breathing, hind-limb paralysis from a clot, or collapse. Early detection through screening echocardiograms and proactive management can add months to years of good-quality life. The signs to watch for are subtle: faster-than-usual resting breathing, weight loss, hiding, or one cold painful back leg.
Last reviewed: May 2026
What Is Cat Hypertrophic Cardiomyopathy?
Cat hypertrophic cardiomyopathy is a disease in which the muscular walls of the left ventricle thicken abnormally, reducing the heart's ability to fill with blood and increasing the risk of congestive heart failure and aortic thromboembolism. About 15 percent of all adult cats and roughly 30 percent of cats over 9 years old have echocardiographic evidence of HCM, making it the single most common feline cardiac disease (Payne et al., 2015, JVIM). Maine Coons, Ragdolls, Sphynx, British Shorthairs, and Persians carry the highest breed risk, with confirmed heritable mutations in Maine Coons (MYBPC3-A31P) and Ragdolls (MYBPC3-R820W).
The disease is often silent for years. A cat may live a full life with mild HCM and never show clinical signs. The danger is the cat that progresses to congestive heart failure (CHF) or throws a clot — both events can be the first warning the owner ever sees, as described in Ettinger's Textbook of Veterinary Internal Medicine.
Early Symptoms of HCM in Cats
Early HCM in cats produces few or no outward signs, which is why screening matters. When subtle signs do appear, owners may notice slightly faster resting breathing, mild lethargy, or reduced jumping. A resting (sleeping) respiratory rate above 30 breaths per minute is the single most useful at-home red flag and warrants vet evaluation within days, not weeks. Some cats lose 5 to 10 percent of body weight quietly over a few months.
A new heart murmur or gallop sound found on a routine physical exam is often the first clue. About one-third of cats with HCM have no audible murmur, however, so a normal exam does not rule out the disease.
Advanced Symptoms — Congestive Heart Failure
Once a cat with HCM progresses to congestive heart failure, the signs become hard to miss and are always an emergency. Rapid breathing at rest (more than 40 breaths per minute), open-mouth breathing, blue-tinged gums, hiding, and refusal to eat are typical. Cats almost never cough with heart disease — coughing is far more likely asthma — so coughing is not a reliable HCM sign in cats. Roughly half of HCM cats that develop CHF do so within 2 to 4 years of diagnosis. Median survival after a first CHF episode is approximately 1.3 years with appropriate treatment (Luis Fuentes et al., 2020, JVIM (ACVIM Consensus on Feline Cardiomyopathies)).
Aortic Thromboembolism — The "Saddle Thrombus"
Aortic thromboembolism (ATE) is HCM's most feared complication: a clot forms in the enlarged left atrium, breaks loose, and lodges where the aorta splits to supply the back legs. Cats present suddenly with paralysis or extreme weakness of one or both hind limbs, painful vocalization, cold pale or blue paw pads, and absent femoral pulses. About 10 to 15 percent of cats with HCM develop ATE during their disease course. Even with intensive care, survival to discharge is only about 30 to 45 percent, and many owners elect humane euthanasia at presentation because of severe pain and a poor long-term prognosis.
How Vets Diagnose Feline HCM
Diagnosis is by echocardiogram (cardiac ultrasound) performed by a cardiologist or experienced sonographer. The heart's wall thickness is measured during diastole; a left ventricular free-wall or septal thickness greater than 6 mm in an adult cat supports the diagnosis. NT-proBNP, a blood biomarker, is useful as a screening test — a low value makes significant HCM unlikely, while an elevated value warrants an echocardiogram. Chest X-rays show congestive failure (pulmonary edema, pleural effusion) but cannot diagnose HCM itself.
Routine senior wellness visits should include a careful cardiac auscultation and resting heart rate, with at-home sleeping respiratory rate counts as a free, sensitive monitoring tool, as outlined in the AAFP-AAHA feline life-stage framework (AAFP-AAHA Feline Life Stage Guidelines, 2021).
Treatment Options
Treatment depends on disease stage. Preclinical HCM with a normal-sized left atrium usually requires no medication — just rechecks every 6 to 12 months. Once the left atrium enlarges, many cardiologists add clopidogrel, an anti-platelet drug, because the risk of clot formation rises sharply. Beta-blockers like atenolol may be used if there is dynamic left ventricular outflow tract obstruction.
In congestive heart failure, furosemide (a diuretic) is the cornerstone of treatment, often paired with pimobendan in select cases and an ACE inhibitor. Once a cat has had CHF, life-long medication is required and home sleeping respiratory rate tracking becomes essential — a sustained rise above 30 breaths per minute usually means edema is returning.
When to See a Vet
Not every symptom is a midnight emergency, but some warrant same-day attention and a few are true ERs. Use the lists below to sort which bucket you're in.
Call your vet today if:
- New heart murmur found on routine exam, especially in an at-risk breed
- Sleeping respiratory rate consistently above 30 breaths per minute
- Subtle weight loss or reduced activity in a cat over age 6
- Cat seems to tire more easily during play or grooming
- Annual wellness lab work has not been done in over a year for a senior cat
Go to the ER immediately if:
- Open-mouth or labored breathing — cats only mouth-breathe when severely distressed
- Sudden hind-limb paralysis, dragging back legs, or crying out in pain
- Cold or blue-tinged back paw pads
- Collapse, fainting, or sudden weakness
- Blue or gray gum color
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Frequently Asked Questions
How long can a cat live with hypertrophic cardiomyopathy?
A cat with mild, preclinical HCM may live a full normal lifespan with no symptoms. Once a cat develops congestive heart failure, median survival is about 1.3 years with treatment, though some live considerably longer. Cats that survive an aortic thromboembolism event have a median survival of roughly 6 months. Survival depends heavily on disease stage at diagnosis, left atrial size, and response to medications.
How much does HCM diagnosis and treatment cost?
A cardiology consult with echocardiogram runs $400 to $800, an NT-proBNP screening blood test is $80 to $150, and chest X-rays are $150 to $400. Monthly medication for a stable cat is roughly $30 to $80, rising to $80 to $200 once heart failure develops and multiple drugs are needed. An emergency hospitalization for acute congestive failure or saddle thrombus typically costs $2,000 to $5,000.
What breeds are most at risk for cat HCM?
Maine Coons, Ragdolls, Sphynx, British Shorthairs, Persians, Norwegian Forest Cats, and Bengals carry the highest documented risk. Maine Coons and Ragdolls have specific MYBPC3 gene mutations linked to HCM; genetic testing is available and many breeders screen. Mixed-breed cats can also develop HCM — about 10 to 15 percent of the general cat population is affected regardless of breed, so screening any cat with a murmur is worthwhile.
What is a "saddle thrombus" in cats and is it survivable?
A saddle thrombus is a blood clot that lodges where the aorta divides to supply the back legs, causing sudden paralysis, severe pain, and cold paws. Survival to hospital discharge is only 30 to 45 percent even with aggressive care. Many cats are humanely euthanized at presentation because of severe pain and a high recurrence rate. Clopidogrel reduces (but does not eliminate) the risk of a first event in cats with enlarged left atria.
Can I screen my cat for HCM at home?
You can monitor a sleeping respiratory rate at home, which is the most useful early-warning tool. Count breaths over 30 seconds while your cat is sound asleep and multiply by two. A sustained value above 30 breaths per minute, or any value above 40, warrants prompt vet evaluation. Definitive diagnosis still requires an echocardiogram performed by a cardiologist.
Should I get genetic testing for my Maine Coon or Ragdoll?
Yes — a cheek-swab genetic test for MYBPC3 mutations is inexpensive (typically $50 to $80) and helps guide screening frequency. A negative genetic test does not rule out HCM (other mutations exist), but a positive test identifies a higher-risk cat who should have baseline and annual echocardiograms starting at 1 to 2 years of age.
Does an ACE inhibitor or pimobendan extend life in preclinical HCM?
Current evidence does not show clear survival benefit from pimobendan or ACE inhibitors in cats with preclinical (asymptomatic) HCM, which is why most cardiologists do not start these drugs until heart failure is documented. Clopidogrel for clot prevention in cats with enlarged left atria does have evidence supporting its use. Treatment plans should be individualized with a cardiologist.
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