HCM and Heart Disease in Cats: Signs, Diagnosis and Outlook

What HCM and cardiomyopathy are

Cardiomyopathy means disease of the heart muscle. VCA Animal Hospitals lists several types in cats, and Cornell Feline Health Center describes hypertrophic cardiomyopathy as the most common heart disease of cats. In HCM the walls of the left ventricle, the heart's main pumping chamber, become abnormally thick. The thickened muscle is stiffer and the chamber holds less blood, so the heart works less efficiently.

Genetics plays a role. Cornell lists higher rates in Maine Coon, Ragdoll, American Shorthair, Sphynx, Bengal, Chartreux, Norwegian Forest, Siberian and Persian cats, among others, though any cat can be affected. VCA notes the heart can also thicken because of another illness, especially hyperthyroidism or high blood pressure, and treating that cause can help or even resolve the heart changes. For many cats no cause is found.

Signs of heart disease in cats

Many cats with HCM show no signs at all, sometimes for years; VCA calls this compensated heart disease. That is why it is often found by chance during a checkup, or only when the disease is advanced. When signs appear, Cornell describes labored or rapid breathing, open-mouth breathing and lethargy, usually caused by fluid building up in or around the lungs. VCA adds that fluid can also collect in the belly, making it look swollen.

The most dramatic sign is a blood clot. Clots can form in the enlarged heart and travel down the main artery, blocking blood flow to the back legs. The cat suddenly cries out in pain, and cannot use one or both back legs. Cornell notes that sudden death is possible but relatively rare. Some cats also simply become quieter, hide more or eat less.

When to call your vet today

Call your vet promptly if your cat seems to tire easily, is less playful, is hiding more or eating less, especially if it belongs to one of the higher-risk breeds or has hyperthyroidism or high blood pressure. If you notice your cat breathing a little faster than usual while sleeping or resting, call for an appointment the same day rather than waiting.

If your cat has been diagnosed with heart disease, ask your vet which signs mean you should call straight away, and keep every recheck appointment. Give all medicines exactly as prescribed and call before stopping or changing anything.

When it's an emergency

Go to your vet or the nearest emergency vet immediately if your cat is breathing fast or with effort while at rest, is breathing with its mouth open, has its belly moving hard with each breath, has blue or very pale gums, or collapses. These signs often mean fluid around the lungs, which can be life-threatening and may need to be drained urgently.

Treat it as an emergency, too, if your cat suddenly cries out, drags or cannot use its back legs, or seems paralyzed in the back end. A blood clot is extremely painful and needs immediate care. Keep your cat calm and quiet in a carrier on the way, and phone ahead so the team is ready.

What you can safely do at home

Do not give any human medicine, including aspirin or other pain relievers, and do not give a cat another pet's heart medicine. Only your vet can choose and adjust heart drugs. Keep a cat that is breathing hard as calm and still as possible and get it to a vet, rather than trying anything at home.

For a cat already diagnosed, keep its environment calm, follow the diet your vet recommends, which VCA notes is often lower in sodium, and avoid salty treats. Ask your vet whether you should count your cat's breathing rate at rest at home and what number should prompt a call, since a change in breathing is often the first sign of trouble.

Your vet may ask you to count breaths while your cat is asleep, which is easiest when it has a familiar cat bed in a quiet spot.

What the vet will likely check

Your vet will listen to the heart and lungs, check heart rate and rhythm, and measure blood pressure. Cornell describes an echocardiogram, an ultrasound of the heart, as the gold standard for diagnosing HCM, with chest X-rays and an electrocardiogram used alongside. Blood tests, including a thyroid test, look for conditions that cause the heart to thicken, which have to be ruled out before HCM is diagnosed. Cornell notes genetic tests exist for some breeds, but not every cat carrying a mutation develops the disease.

There is no cure for HCM. Treatment aims to control the heart rate, relieve fluid on the lungs and reduce the risk of clots, using medicines your vet chooses for your cat. Fluid may be drained from the chest or belly when needed. Cornell reports that newer treatments are being studied but are not yet proven.

Outlook and screening

The outlook varies widely. Cornell notes that cats without signs may live for years with mildly affected hearts, while heart failure, blood clots and low body temperature point to a poorer outlook. VCA notes that HCM with no underlying cause may stay stable for several years, and that treating a cause such as hyperthyroidism can improve or resolve heart changes.

Because many cats show no signs, regular checkups matter, especially for higher-risk breeds and older cats. Ask your vet whether a heart scan makes sense for your cat, and before breeding, ask about screening. Feeding a complete commercial diet ensures enough taurine, a nutrient whose deficiency VCA links to a different, now rare form of heart disease.

This page is general information, not veterinary advice, and it cannot replace an examination by the vet who knows your pet.