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Hypertrophic Cardiomyopathy

Hypertrophic Cardiomyopathy (HCM) is the most common heart disease in cats. In HCM, the heart muscle becomes excessively thickened and scarred. If the disease progresses, fluid can build up in or around the lungs, causing compromised breathing. Affected cats may also be predisposed to serious blood clots. HCM may be associated with hyperthyroidism (overactive thyroid) or systemic hypertension (high blood pressure) so it is important to test for these in affected cats.

HCM can be inherited in some breeds, notably Ragdolls, Norwegian Forests and Maine Coons, but any type of cat can be affected. Although HCM is the most common heart condition we see in cats, its severity can vary, and many other heart diseases can also occur. Accurate diagnosis of the problem is important so that we can give the most appropriate treatment and prognosis.


In the early stages of HCM, there may be no clinical signs at all. A problem may only be suspected after
examination by a vet. Presence of a murmur or gallop rhythm may be noted on clinical exam, however is not present in all cases.

In the later stages of the disease, the most common clinical sign is a change in breathing – laboured or fast breathing. Changes may be subtle at first, but can become serious quickly, especially in stressed cats. Open mouth breathing is abnormal in cats, unlike panting commonly seen in dogs, and is a sign of extreme respiratory compromise.

Lethargy is seen in some cats, but may be difficult to appreciate due to the sedentary lifestyle of many cats. If a blood clot develops, your cat may suddenly become painful in, or lose the use of one or more limbs.
As many cats do not show any clinical signs until the very late stages of the disease, it is important to investigate any cat that is found to have a murmur or a gallop rhythm, even if they are symptomless.


The gold standard test for HCM in cats is echocardiography. This is where ultrasound is used to examine the heart. It is also known as an “echo” or a heart scan. It is a non-painful and non-invasive procedure for your cat and most pets tolerate it without needing sedation.

Other tests may include:

  • Chest x-rays - to assess for fluid building up on or outside of the lungs, and to check for other causes of breathing problems e.g. lung disease.
  • ECG - if an arrhythmia is suspected.
  • Blood pressure measurement.
  • Blood tests - to assess for thyroid or other systemic issues.


Treatment will depend on what stage of disease your pet is in.

Some cats with HCM may never need any treatment; instead it may be recommended that the condition
is monitored with periodic check-ups. Others may benefit from medications to help control their blood pressure or heart rate, to prevent clots, to improve their heart contractility, or to remove excess fluid from the lungs. Some cats may also need fluid drained from their chest occasionally.

We realise that some cats are hard to medicate - if you are struggling to give your cats medication, let us know and we will try to offer tailored alternatives where possible. Treatment is always aimed at giving your cat the best possible quality of life, and keeping them happy and symptom free for as long as possible.


Prognosis is very variable for cats with HCM. Some cats may live for many years with appropriate medical management, where some with more severe disease may only manage for a short period – especially if they present with symptoms at a late stage of disease. Once treatment begins, it may be advised to monitor your cat in case adjustments are needed to their dose.

You may be asked to monitor sleeping respiratory rate (SRR), as well as attend the clinic for repeat check-ups at occasional intervals.

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