Cardiomyopathy: Understanding Heart Disease in Cats

In this guide

Cardiomyopathy is the umbrella term for any disease affecting the heart muscle itself, and it is the leading cause of heart failure in cats. Unlike humans and dogs, cats rarely suffer from diseased heart valves; their heart problems almost always originate in the muscle.

The four types

• Hypertrophic cardiomyopathy (HCM) — the most common form, where the heart wall thickens, reducing the volume of blood the heart can hold and preventing it from relaxing properly between beats.
• Dilated cardiomyopathy (DCM) — the heart wall thins, the chambers enlarge, and the muscle loses its ability to contract effectively.
• Restrictive cardiomyopathy (RCM) — fibrosis stiffens the heart wall, stopping the chambers filling normally.
• Intermediate cardiomyopathy (ICM) — a mixture of features from more than one type, such as both thickening and dilation.

What causes it?

In most cats the underlying trigger is never identified, but recognised causes include secondary conditions such as hyperthyroidism, hypertension and acromegaly; nutritional taurine deficiency, which drives dilated cardiomyopathy; infiltration of the heart muscle by tumours such as lymphoma; toxic side effects from certain drugs; and inherited genetic defects, notably in Maine Coons and some other pedigree breeds.

How the disease affects the heart

With HCM and RCM, the problem lies mainly in the heart's relaxation phase (diastole), so it cannot fill with blood efficiently; if this worsens, it leads to diastolic heart failure. With DCM, the problem is contraction (systole), compromising the heart's ability to pump blood out, which can progress to systolic heart failure.

Early warning signs

Many cats show no symptoms at all in the early stages, and some never progress to clinical disease, while others deteriorate quickly. Because cats are rarely walked or exercised the way dogs are, reduced stamina is easy to miss; owners may only notice a cat resting more than usual. A vet may pick up early clues during a routine check-up, which is one reason annual examinations matter, including:

• A heart murmur — an abnormal sound caused by turbulent blood flow.
• A gallop rhythm — an extra, abnormal third heart sound.
• Abnormal heart rate, too fast, too slow, or with beats that produce no detectable pulse.
• Rhythm disturbances caused by interference with the heart's normal electrical impulses.

When heart failure develops

Once cardiac function is significantly impaired, congestive heart failure follows, with reduced blood flow and output. Some cats deteriorate very suddenly. Collapse or fainting is uncommon but can occur with serious rhythm disturbances that starve the brain of oxygen. The clearest sign in cats is laboured or rapid breathing, caused either by fluid around the lungs (pleural effusion) or fluid within the lungs (pulmonary oedema). Cold ears and paws, pale gums, and occasionally a bluish tinge to the gums, eyes or skin can also appear. Unlike dogs, cats rarely cough with heart disease; coughing is more likely to point to airway disease such as bronchitis.

Feline aortic thromboembolism (FATE)

A blood clot can form inside the heart, usually in the left atrium, because blood is not flowing normally through it. If this clot breaks free, it becomes an embolus and can lodge in small arteries, most commonly near where the aorta divides to supply the back legs. This causes sudden paralysis of one or both hind legs, along with severe pain and distress, and is seen most often alongside HCM.

Diagnosis

• Electrocardiogram (ECG) — useful mainly for detecting rhythm disturbances.
• X-rays — show changes in heart size and shape, and reveal fluid build-up; repeat films can track treatment progress.
• Echocardiography (heart ultrasound) — the only test that reliably distinguishes between the different types of cardiomyopathy, and is well tolerated without sedation in most cats.
• Additional blood tests or blood pressure checks — used to investigate underlying disease where relevant.

Treatment

The root cause is rarely treatable directly, though managing an underlying condition such as taurine deficiency, hypertension or hyperthyroidism can improve heart function. Once heart failure sets in, drug treatment can help manage the condition, including beta-blockers (atenolol, propranolol) to slow the heart and reduce its oxygen demand; diltiazem, a calcium-channel blocker that eases the heart's workload; ACE-inhibitors or ARBs, which block a hormone system that drives heart disease; pimobendan, which strengthens contractions and dilates blood vessels; and diuretics such as furosemide, which are especially valuable for clearing fluid build-up once congestive failure develops.

No single drug protocol is proven definitively effective across all cats, and more research is needed, but diuretics remain the mainstay for managing congestive signs. Early diagnosis gives the best chance of slowing progression and preserving a good quality of life.

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