Glossary

Hypertrophic cardiomyopathy

The most common feline heart disease, in which the wall of the main pumping chamber thickens and the heart works less well.

Also called: HCM, feline HCM, thick heart muscle, heart disease in cats

Hypertrophic cardiomyopathy, or HCM, is a disease in which the muscle wall of the left ventricle becomes thick and stiff. The heart then fills poorly and can pump less blood. It is the most common heart disease in cats. It appears in mixed-breed cats and is more common in some breeds, including the Maine Coon, Ragdoll, British Shorthair and Sphynx. DNA tests exist for gene changes in a few breeds, but a clear test does not rule out the disease.

Many cats with HCM show no signs for years. Some develop fast or labored breathing, open-mouth breathing, tiredness or fainting, as fluid collects in or around the lungs. A heart murmur or an irregular rhythm can be picked up at a wellness exam. Others first show signs when a blood clot forms, see arterial thromboembolism, and a few die suddenly.

Diagnosis needs an ultrasound of the heart by a vet with the right training, called an echocardiogram. Vets must also rule out conditions that thicken the heart too, such as hyperthyroidism and high blood pressure. Treatment is tailored to the stage and may include heart and anti-clotting medicines. A cat breathing quickly while resting needs a vet at once. Ask your vet about screening if your breed is at risk.

Last reviewed November 7, 2026

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Related terms

Arterial thromboembolism A blood clot that lodges in an artery, most often cutting off blood to a cat's back legs and causing sudden pain and paralysis. Blood pressure The force of blood against artery walls; high readings in cats usually come from another disease and can damage the eyes, brain, heart and kidneys. Hyperthyroidism A common disease of older cats in which an overactive thyroid speeds up the body, causing weight loss despite a big appetite. Blood panel A set of blood tests that counts cells and measures chemicals to show how a cat's organs are working. Wellness exam A routine vet visit for a healthy-looking cat to check its body, update vaccines and parasite control, and catch problems early.

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