Hypertrophic Cardiomyopathy in Cats: Signs, Diagnosis and Treatment

By Tailwisp Editorial TeamUpdated October 20, 20264 min read

Heart disease in cats is often silent. A cat can look completely healthy and still have a thickened heart. Hypertrophic cardiomyopathy, usually shortened to HCM, is the most common heart disease in cats, and learning the warning signs could save your cat's life.

What is HCM?

In HCM, the muscular walls of the heart's left ventricle thicken. The thicker muscle stiffens the heart, so it cannot relax and fill properly. Over time, the pressure builds up in the left atrium, and the heart may enlarge. This can lead to:

• Congestive heart failure, in which fluid builds up in or around the lungs
• Arterial thromboembolism, in which a blood clot forms in the heart and lodges in an artery, often at the back legs
• Arrhythmias and, rarely, sudden death

Who is at risk?

HCM can affect any cat, though it is more common in middle-aged and older male cats. Some breeds have inherited forms:

• Maine Coon
• Ragdoll
• British Shorthair
• Sphynx
• Persian
• Other breeds and domestic cats

Genetic tests exist for certain mutations in Maine Coons and Ragdolls, though a negative result does not rule out HCM. Responsible breeders screen their cats with heart ultrasounds.

Other conditions, such as hyperthyroidism and high blood pressure, can thicken the heart and must be ruled out. See hyperthyroidism in cats.

Signs

Many cats have no signs for years. When signs appear, they may include:

• Fast or labored breathing, even at rest
• Open-mouth breathing or panting, which is never normal in cats
• Lethargy, hiding and reduced appetite
• Coughing, less common than in dogs
• Sudden collapse
• Cold, painful, paralyzed hind legs, with pale paw pads, from a clot

Emergencies

Go to an emergency vet immediately if your cat:

• Breathes with an open mouth or has labored breathing
• Suddenly cannot use the back legs and cries in pain
• Collapses or has blue-gray gums

See the emergency warning signs guide.

Counting breaths at home

A simple home test can alert you early. When your cat is asleep or resting calmly, count the number of breaths in one minute. A breath is one rise and fall of the chest. Normal is typically below about 30 breaths per minute. If the rate is consistently higher, call your vet. Keep a log, especially if your cat has heart disease.

Diagnosis

• Physical exam. The vet may hear a heart murmur, gallop sound or irregular rhythm, though some cats with HCM have none, and some healthy cats have murmurs.
• Echocardiogram. A heart ultrasound by a veterinary cardiologist is the best test.
• Chest X-rays. Show heart size and fluid in the lungs.
• Blood pressure and blood tests. Check for thyroid and kidney disease.
• ECG. Detects abnormal rhythms.
• NT-proBNP blood test. A screening aid.

Asthma and other lung disease can cause similar breathing signs. See feline asthma.

Treatment

There is no cure, but treatment can control signs and improve quality of life. Your vet or cardiologist may prescribe:

• Diuretics to remove excess fluid
• Heart medications to help the heart relax or slow the rate
• Blood thinners to reduce the risk of clots
• Oxygen and hospitalization in a crisis
• Treatment of any other disease, such as hypertension or hyperthyroidism

Cats with mild disease and no signs may need only monitoring.

Living with HCM

• Give medicines exactly as directed. See how to give a cat a pill.
• Keep stress low and routines calm.
• Feed a good diet and keep a healthy weight. See how to help an overweight cat lose weight.
• Count breathing rate regularly.
• Attend scheduled rechecks, often every six to twelve months.
• Keep the cat indoors and safe.

Outlook

Outlook depends on severity. Some cats with mild HCM live normal lifespans. Those with heart failure or clots have a more guarded outlook, though some do well for months or years with treatment.

Screening and breeding

If you plan to buy a pedigree kitten, ask for evidence of heart screening in the parents, including echocardiograms and genetic tests where available. Ethical breeders are open about results. Ask your vet when to start screening your own cat, especially for high-risk breeds. See how to choose a cat breed.

When to see a vet

See a vet if you hear of a murmur, notice fast breathing or if your cat is a high-risk breed. Use the US vet directory to find a clinic, and see cat vet visit costs. Seniors should have regular checkups. See senior cat care guide.

This article is general educational information, not veterinary advice. Every cat is different. If your cat is unwell, or you are unsure about a symptom, diet change or medication, contact your veterinarian.