HCM in Cats: Feline Heart Disease Explained
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Hypertrophic cardiomyopathy (HCM) is the most common heart disease in cats — the heart's muscular walls thicken, so the heart can't fill and pump efficiently. It's often silent until it's advanced, which is why the first clue can be a heart murmur at a checkup or, in serious cases, sudden breathing trouble or a painful back-leg. It can't be cured, but many cats are managed well for years, and early detection makes a real difference.
Emergency red flags
Get to an emergency vet immediately if your cat has: fast or labored breathing, open-mouth breathing or panting, sudden weakness or collapse, or a suddenly painful, cold, or paralyzed hind leg (often crying out). These can mean fluid in the lungs (heart failure) or a blood clot lodged in the leg — both are life-threatening and time-critical.
A resting or sleeping cat should breathe smoothly and quietly. Panting like a dog is not normal for a cat and always warrants urgent attention.
What HCM is
In HCM, the muscular walls of the heart's main pumping chamber (the left ventricle) become abnormally thick. A stiff, thickened heart can't relax and fill with blood properly, so pressure backs up and the heart works less efficiently. Over time this can lead to congestive heart failure (fluid in or around the lungs) or dangerous blood clots.
It's frequently linked to genetics — some breeds such as Maine Coons and Ragdolls are predisposed — but it also occurs in ordinary domestic cats. It can develop at almost any age.
Signs to watch for
The hardest part of HCM is how quiet it often is. Many cats show no signs until the disease is advanced. When signs do appear, watch for:
- Faster or harder breathing at rest, or open-mouth breathing
- Lethargy and reduced activity or appetite
- Hiding or reluctance to move
- Sudden hind-limb weakness or pain from a clot (a feline aortic thromboembolism, or "saddle thrombus")
- Fainting or collapse in some cases
A heart murmur or an abnormal rhythm found on a routine exam is often the first hint — but not all cats with HCM have a murmur, and not all murmurs mean HCM.
How it's diagnosed
Diagnosis centers on imaging the heart:
| Test | What it shows |
|---|---|
| Echocardiogram (heart ultrasound) | The definitive test — measures wall thickness and how the heart fills and pumps. |
| proBNP blood test | A screening marker that can flag heart strain and help decide who needs an echo. |
| Chest X-rays | Detect fluid in or around the lungs (heart failure). |
| Blood pressure & thyroid tests | Rule out high blood pressure and hyperthyroidism, which can thicken the heart too. |
Your vet will also listen for murmurs, gallops or abnormal rhythms and check the breathing rate at rest.
Treatment and why tracking helps
HCM can't be reversed, but treatment aims to keep the heart working and prevent complications:
- Medications to ease the heart's workload, manage heart failure (including diuretics if fluid builds up), or reduce clot risk, as your vet directs.
- Treating underlying causes like high blood pressure or hyperthyroidism when present.
- Regular rechecks and echocardiograms to adjust the plan as the disease changes.
Practical take: One of the most useful things you can do at home is count your cat's resting (sleeping) breathing rate — breaths per minute while asleep. A steady climb over days is one of the earliest signs of heart failure, often before a cat looks sick. Ask your vet what number to watch for your cat, and log it over time so a rising trend stands out.
Catch heart failure before the crisis
Tavi logs your cat's resting breathing rate, weight, energy and medications and charts them over time — so a slow climb in breaths per minute, an early sign of heart failure, shows up before it becomes an emergency. Free for your first pet.
Frequently asked questions
What are the signs of heart disease in cats?
HCM is often silent until advanced. When signs appear, watch for faster or labored breathing at rest, open-mouth breathing, lethargy, hiding, and sudden hind-leg weakness or pain from a blood clot. A heart murmur found at a checkup is frequently the first clue, so don't skip routine exams.
How long can a cat live with HCM?
It varies widely by how advanced the disease is at diagnosis. Cats with mild HCM and no symptoms may live many years, while those who have already had heart failure or a clot have a more guarded outlook. Early detection, regular echocardiograms and consistent treatment give the best results.
What is a normal resting breathing rate for a cat?
A healthy cat usually breathes comfortably and quietly while resting or asleep, generally under about 30 breaths per minute. A steadily rising sleeping breathing rate can be an early sign of heart failure. Ask your vet for your cat's target and track it so an upward trend is easy to spot.
Can HCM in cats be cured?
No, HCM can't be cured or reversed, but it can be managed. Medications ease the heart's workload, treat heart failure, and reduce the risk of dangerous clots, while treating any underlying high blood pressure or thyroid disease helps. Regular rechecks let your vet adjust the plan over time.
What is a saddle thrombus in cats?
A saddle thrombus, or feline aortic thromboembolism, is a blood clot that lodges where the aorta splits to the hind legs, often as a complication of HCM. It causes sudden pain, weakness or paralysis of one or both back legs, cold limbs, and crying out. It's a life-threatening emergency needing an immediate vet.
Tavi's guides are informational and not a substitute for professional veterinary advice, diagnosis or treatment. When in doubt, call your veterinarian. Sources: Cornell University Feline Health Center; American College of Veterinary Internal Medicine (ACVIM); VCA Animal Hospitals; Merck Veterinary Manual