Hypertrophic Cardiomyopathy (HCM)
Learn what the condition is, how it may be detected early, how it is treated or managed, and which breeds or species are linked to it.
Condition snapshot
A concise guide to the condition’s pattern, detection, management and urgency.
Emergency presentation is possibleOpen-mouth breathing, collapse or sudden painful hindlimb weakness or paralysis requires emergency care.
This snapshot is a general guide, not a diagnosis or treatment plan. New, severe or worsening signs require veterinary assessment.
About the condition
Hypertrophic cardiomyopathy, or HCM, is the most common primary heart muscle disease in cats. The muscular walls of the left ventricle become abnormally thick, which makes the chamber less able to relax and fill normally between beats. The thickened muscle can also alter blood flow through the heart and increase pressure in the left atrium.
Some cats remain symptom-free for years. Others develop congestive heart failure, where fluid accumulates in or around the lungs, or arterial thromboembolism, where a blood clot leaves the heart and blocks circulation to a limb. Sudden death can occur. A murmur, gallop rhythm or fast heart rate may be detected, but importantly, some cats with significant HCM have no abnormal heart sound.
Breathing changes are among the most important warning signs. Increased sleeping respiratory rate, laboured breathing or open-mouth breathing can indicate heart failure. Sudden painful weakness or paralysis of one or both hind legs can indicate a clot and is an emergency.
HCM has a genetic basis in some family lines, including recognised variants in Maine Coons and Ragdolls, but known mutations explain only part of feline HCM. A negative DNA result cannot rule out the disease. High blood pressure and hyperthyroidism can also cause heart thickening and must be considered.
It measures wall thickness, chamber size, relaxation and blood-flow patterns. The long-term outlook ranges from a normal lifespan in mildly affected cats to severe progressive disease when heart failure or thromboembolism develops.
Apparent wall thickening can reflect normal muscular variation, dehydration or a secondary disease rather than primary hypertrophic cardiomyopathy. Wall thickness exists within a wider context of age, blood pressure, thyroid status, hydration and overall cardiac structure rather than as an isolated number.
Screening & Early Detection
Routine auscultation can identify a murmur, gallop rhythm or abnormal heart rate, but a normal stethoscope examination does not exclude HCM. Cats with a family history, an abnormal heart sound or breeds with recognised increased risk may benefit from echocardiographic screening, particularly before breeding.
Echocardiography performed by an experienced veterinarian or cardiologist is the most useful screening and diagnostic tool because it directly measures heart-wall thickness and chamber size. Cardiac biomarkers such as NT-proBNP can provide additional information when imaging is not immediately available, but they do not replace an echocardiogram for definitive assessment.
Blood pressure and thyroid hormone should be checked when heart thickening is found, especially in older cats, because hypertension and hyperthyroidism can produce secondary changes that resemble HCM. Breed-specific DNA tests can identify particular known variants in Maine Coons and Ragdolls, but a negative result does not mean the cat is free of all inherited HCM risk.
At home, a sleeping respiratory rate that is repeatedly higher than the cat’s usual baseline, new breathing effort, collapse or sudden hindlimb weakness requires prompt assessment. Cats known to have HCM need repeat echocardiography and monitoring at intervals based on severity.
Echocardiography is the main test used to diagnose HCM and assess severity.
Treatment & Management
Treatment is based on the cat’s actual heart findings rather than the diagnosis alone. A cat with mild HCM and no atrial enlargement or clinical signs may need monitoring without medication. When congestive heart failure develops, diuretics are used to remove excess fluid, and additional drugs may be selected according to blood pressure, heart rate and outflow obstruction.
Cats with significant left atrial enlargement have an increased risk of arterial blood clots. Antiplatelet medication such as clopidogrel may be prescribed to reduce that risk. A cat arriving in respiratory distress is handled with minimal stress, given oxygen and stabilised before non-essential testing.
Home monitoring of sleeping respiratory rate is extremely useful after heart failure has occurred because an upward trend can provide early warning of recurrent fluid accumulation. Medication doses should not be changed without veterinary guidance, particularly diuretics, because kidney function and hydration must remain balanced.
There is no treatment that makes inherited HCM disappear, but many cats remain stable for long periods. Prognosis depends heavily on left atrial enlargement, heart failure, clot formation and rhythm abnormalities. Breeding decisions should use echocardiographic findings and available breed-specific genetic information rather than relying on one DNA result alone.
Breeds or species affected
American Shorthair
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Bengal
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British Longhair
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British Shorthair
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Cornish Rex
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Devon Rex
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Exotic Shorthair
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Himalayan
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Maine Coon
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Minskin
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Norwegian Forest Cat
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Persian
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RagaMuffin
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Ragdoll
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Scottish Fold
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Scottish Straight
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Selkirk Rex
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Siberian
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Sphynx
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Toyger
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Turkish Angora
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Turkish Van
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Bambino
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Cheetoh
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Dwelf
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Elf Cat
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