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Health and vet care

Hypertrophic cardiomyopathy (HCM)

Also called HCM, Feline hypertrophic cardiomyopathy

Updated

What is hypertrophic cardiomyopathy (HCM) in cats?

Hypertrophic cardiomyopathy, or HCM, is a disease in which the muscular walls of a cat's heart thicken, especially around the main pumping chamber, so the heart works less efficiently. The Cornell Feline Health Center calls it the most common heart disease in cats. Many affected cats look well, and it is diagnosed with an echocardiogram.

What happens to the heart in HCM?

The muscle in the heart's walls grows thick, most of all around the left ventricle, the chamber that pumps blood out to the body. A thick, stiff chamber fills less well, so the heart has to work harder to do the same job.

The disease usually gets worse over time, but how fast varies a lot. Cornell notes that cats with no signs can live for years with only mildly reduced heart function.

Which signs mean a cat needs a vet right away?

Many cats with HCM do not look ill, which is why it can go unnoticed. When it does cause trouble, the signs are those of heart failure or a blood clot, and both are emergencies.

Labored, rapid or open-mouth breathing, or unusual lethargy, can mean fluid is building up. Sudden pain, weakness or paralysis in the back legs can mean a clot has blocked blood flow to them. Take the cat to a vet or emergency clinic at once. Sudden death is possible, though Cornell describes it as relatively rare.

How is HCM diagnosed?

With echocardiography, an ultrasound scan that shows the heart's walls and chambers. A vet also checks for other causes of thick heart muscle, such as high blood pressure and an overactive thyroid, before calling it HCM. Only a vet can diagnose it; this page only describes it.

Which breeds are linked to HCM?

Cornell lists a higher prevalence in several breeds, including the Maine Coon, Ragdoll, British Shorthair, American Shorthair, Sphynx, Bengal, Chartreux, Norwegian Forest Cat, Siberian and Persian, and says genetics plays a role. A breed link raises the odds. It does not mean cats outside those breeds are safe.

What does the Ragdoll gene test show?

In Ragdolls, a variant of the MYBPC3 gene called R820W is linked to HCM. A university veterinary genetics lab offers a test that reports whether a cat carries no copy, one copy or two copies of it.

Two copies carry the highest risk. In a 2014 survey of 236 tested Ragdolls (Borgeat and colleagues, Journal of Veterinary Cardiology), the 12 cats with two copies had a median survival of 5.65 years, against more than 15 years for cats with one copy or none.

A clear result does not rule HCM out. The test looks for one known variant, and cats without it can still develop the disease.

What to look for

  • Labored, rapid or open-mouth breathing while resting
  • Unusual tiredness, hiding or reluctance to move
  • Sudden pain, weakness or dragging of one or both back legs
  • For a Ragdoll, whether the breeder can show the parents' gene test results

Reading a clear gene test as a healthy heart

The Ragdoll test checks one variant in one gene. A cat without it can still develop HCM, so a clear result is not a heart check. Only an echocardiogram shows what the heart itself looks like.

Questions about hypertrophic cardiomyopathy (HCM)

Can a cat with HCM look completely healthy?

A cat with HCM can look completely healthy. Cornell notes that many cats with HCM do not appear ill. Some are only found when a vet listens to the heart or orders a scan, and some show no sign until heart failure or a blood clot, which is why regular checkups matter.

Is open-mouth breathing in a cat an emergency?

Open-mouth breathing in a cat at rest should be treated as an emergency. Cats rarely breathe with their mouths open at rest, and labored or open-mouth breathing is one of the signs of heart failure. See a vet or an emergency clinic straight away.

Should I ask about HCM when getting a Ragdoll?

Anyone getting a Ragdoll should ask about HCM. Ask the breeder whether both parents were DNA tested for the Ragdoll gene variant and whether they had heart scans, and ask to see the results. Then ask your own vet whether heart screening makes sense for your cat as it grows.

Where this comes up

Sources