In a cat, heart disease most often means cardiomyopathy, a disease of the heart muscle, and the commonest form thickens the wall of the heart. Cornell's Feline Health Center says many cats with that form live normal or near-normal lifespans, and many show no signs early on. Fast or labored breathing, or back legs that suddenly stop working, is an emergency.
Cardiomyopathy means disease of the heart muscle. Cornell says it accounts for almost two-thirds of the heart conditions found in cats. In the commonest form, hypertrophic cardiomyopathy or HCM, the muscle of the left ventricle, the heart's main pump, grows thick. The chamber holds less blood and cannot relax properly.
Cornell says HCM affects up to 15% of cats. A 2020 consensus statement from the American College of Veterinary Internal Medicine (ACVIM) gives about 15% for cats in general and up to 29% for older cats. Cornell names the Maine Coon, Ragdoll, Sphynx, British Shorthair, Chartreux and Persian as breeds at higher risk.
There are other forms. In restrictive cardiomyopathy scar tissue keeps the muscle from relaxing fully, and in dilated cardiomyopathy the wall is thin and the pump is weak. The Merck Veterinary Manual says the dilated form became far less common after 1987, when a lack of taurine was found to cause most cases and taurine was added to all commercial cat foods.
Fluid can collect in or around the lungs, which is congestive heart failure. A clot can also form in the enlarged upper chamber of the heart, break up and block an artery, most often the ones that supply the back legs.
A vet may hear a murmur at a routine visit, but a murmur settles little. The ACVIM statement says a murmur has been reported in up to 80% of cats that have HCM without signs, and in 30% to 45% of healthy cats without HCM. The Merck manual says at least one in three cats with HCM has no murmur.
The signs of heart failure, Cornell says, are rapid or labored breathing, breathing with the mouth open, lethargy and a poorer appetite. It counts more than 35 breaths a minute at rest as a raised breathing rate. For a cat being treated for heart failure, the ACVIM statement asks owners to count the breaths while the cat rests or sleeps, aiming to stay under 30 a minute.
A clot shows as sudden lameness or paralysis of the back legs, usually with severe pain. Cornell also says cats with HCM are at risk of sudden death, though that is relatively rare.
| Test | What it looks at | What it tells the vet |
|---|---|---|
| Listening to the heart | Murmurs and other abnormal sounds. | A reason to look further. Cornell says a stethoscope cannot detect all feline heart diseases. |
| Heart ultrasound, or echocardiogram | The thickness of the walls and the size of the chambers, as a moving picture. | Cornell and the ACVIM statement both call it the gold standard for finding cardiomyopathy. |
| Chest x-rays | The lungs and the outline of the heart. | Cornell says they show whether heart failure is present. The ACVIM statement says they are poor at finding mild or moderate heart changes. |
| NT-proBNP blood test | A protein the heart releases when it is enlarged. | Cornell says it can pick out cats that need more tests, but cannot prove heart disease by itself. |
| Blood pressure and thyroid test | High blood pressure and an overactive thyroid. | Cornell says both can lie behind heart muscle disease, and must be ruled out before a vet can call it HCM. |
Petipedia explains x-rays and ultrasound and the blood test.
Cornell says nothing is known to make HCM go away, but that a care plan can help manage the signs. What is done depends on the stage, and the ACVIM statement sets the stages out:
The diuretic is typically furosemide. The label of Salix, a furosemide tablet, covers dogs and cats and says it treats the fluid buildup that comes with a failing heart.
On 14 March 2025 the FDA conditionally approved Felycin-CA1 (sirolimus) for cats whose heart wall is thickened by HCM but who show no signs. The FDA calls it the first product approved for cats with HCM for any use. It is given once a week on prescription, and both the FDA and the label say it should not be used in cats with liver disease or diabetes. Conditional approval means the company has shown a reasonable expectation that the drug works but has not yet proven it to the FDA's full standard.
The paperwork for Vetmedin (pimobendan) says it is for dogs only. Its one mention of cats is a warning to keep it out of their reach, and it says not to give it in hypertrophic cardiomyopathy. The ACVIM statement says it could be considered for some cats in heart failure. That is a use outside the label, which the FDA says the law allows only on a vet's order. Petipedia's page on the drug is What is Vetmedin?
The ACVIM statement also says unnecessary medications should be avoided, and foods high in salt too.
The ACVIM statement says most cats with HCM have no signs, and that about 23% die of their heart disease within five years. Once heart failure develops, Cornell calls the outlook guarded, with expected median survival times between 2 and 12 months. A median is the middle value: half the cats live longer.
Cornell says cats that have had a clot generally have a guarded to poor outlook, and the ACVIM statement says most cats brought to a general practice with a clot are euthanized. One form has a much better outlook, Cornell says: a thickening that is usually seen in younger cats and resolves on its own.
Cornell gives $200 to $400 as the usual cost of a heart ultrasound, on a page that carries no date, so ask the clinic for today's price. The ACVIM statement suggests a recheck every 2 to 4 months for a cat that has had heart failure. See what a vet bill costs, what to do when you cannot pay it and what pet insurance pays for.
Cornell's rule is short: if a cat is struggling to take in air or cannot move its back legs, seek help right away. Go now for breathing with the mouth open, fast or labored breathing at rest, or back legs that are suddenly weak, dragging or painful.
Keep the cat calm, call the clinic to say you are coming, and see Cats: is this an emergency?
If something here is out of date, tell us at hello@petipedia.io and we fix it the same day.
Sources read on 2 October 2026; every number is as the source gives it. Cornell's page on diagnosis carries no date, so its price may be old. The ACVIM statement was read in the open-access copy held by the Royal Veterinary College.