Hypertrophic Cardiomyopathy (Heart Disease) in Cats

Many cats with hypertrophic cardiomyopathy show no signs, particularly in the early stages. When symptoms do occur, they are often subtle and can be easy to miss.  However, while in some cats the disease progresses slowly, in others, it can be quite rapid.  

Common signs include lethargy, increased sleeping, or a reluctance to exercise or play. Some cats may hide more than usual or seem quieter than normal. 

As the disease progresses, breathing changes may become more apparent. This can include rapid breathing, increased effort when breathing, or in more severe cases, open mouth breathing. These signs may indicate fluid build-up within or around the lungs. 

One possible complication is a specific type of blood clot, called an aortic thromboembolism, which can cause sudden pain and weakness or paralysis in the back legs. Cats may cry out, be unable to stand, and have cold hind limbs. 

In some cases, the first sign of HCM may be sudden collapse or sudden death. 

Contact your vet if you notice any changes in your cat’s breathing, behaviour, or activity levels, even if they seem mild. Early signs of heart disease can be easy to overlook. 

Arrange a routine appointment if your cat shows reduced energy, increased sleeping, hiding, or a decreased interest in play or eating less. 

Seek emergency veterinary care immediately if you notice rapid breathing, increased effort when breathing, or any episodes of open mouth breathing. These signs may indicate fluid build-up around the lungs and can become life threatening. 

Seek emergency veterinary care immediately if your cat shows sudden weakness, collapse, or difficulty using their back legs. Signs of pain, vocalisation, or cold hind limbs may indicate a blood clot and require urgent treatment. 

If you are unsure, it is safest to have your cat assessed. Heart disease can progress without obvious signs. 

Diagnosis often begins with a clinical examination. Your vet may detect a heart murmur, an irregular heart rhythm, or an increased heart rate. Some cats with HCM have a normal examination. 

If heart disease is suspected, further tests are recommended. The most useful test is an ultrasound scan of the heart, known as an echocardiogram, which assesses the structure and function of the heart. 

An electrocardiogram (ECG) may be used to assess heart rhythm. Chest X-rays or ultrasound can help identify fluid within or around the lungs. Blood pressure measurement is important, as high blood pressure can cause similar changes to the heart. 

Blood tests may be used to support the diagnosis or identify underlying conditions, including thyroid disease. A cardiac biomarker test can be used as a screening tool but does not replace an echocardiogram. 

Screening may be recommended in higher risk breeds or in cats with a family history of heart disease. 

Treatment depends on the severity of the disease and whether complications are present. Some cats with mild changes and no symptoms may not require immediate treatment but should be monitored. 

When treatment is required, the aim is to reduce the workload on the heart, manage symptoms, and reduce the risk of complications. 

Medications may be used to improve heart relaxation and filling, and to control heart rate or rhythm. In cats at risk of blood clots, anti-clotting medication may be prescribed to reduce the risk of an aortic thromboembolism. 

If fluid build-up occurs around the lungs, diuretics are used to remove excess fluid and improve breathing. In more severe cases, hospitalisation may be required for oxygen therapy and monitoring. 

Any underlying conditions, such as high blood pressure or thyroid disease, should also be treated. 

Treatment is usually ongoing, with regular check-ups to monitor progression and adjust medication. 

Further reading: Hyperthyroidism in Cats

HCM cannot be reliably prevented, as it is often linked to genetic factors. However, early detection and management can reduce the risk of complications. In predisposed breeds such as Maine Coons and Ragdolls, screening may be recommended. This can include routine heart scans to detect changes before symptoms develop. 

Regular veterinary check-ups are important for all cats. Early detection of a heart murmur or other abnormality allows for monitoring and timely intervention. 

Managing other health conditions, including high blood pressure and thyroid disease, is also important in reducing secondary effects on the heart. 

For breeding cats, those with HCM or a strong family history should not be bred from. 

The outlook for cats with hypertrophic cardiomyopathy varies depending on disease severity and the presence of complications. 

Some cats with mild disease may live for many years without clinical signs and maintain a good quality of life with minimal intervention. 

Cats with more advanced disease, or those that develop complications such as fluid build-up or blood clots, have a more guarded outlook and often require ongoing treatment. 

Complications such as heart failure or aortic thromboembolism can affect both quality of life and life expectancy. However, with appropriate treatment and monitoring, many cats can still enjoy a good quality of life for a period of time. 

Regular reassessment is important, as the condition can change over time.