Heart Disease (Hypertrophic Cardiomyopathy) in Cats

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4 min read

Key takeaways

Hypertrophic cardiomyopathy (HCM) in cats is the thickening of the heart muscle resulting in reduced internal volume of the heart chambers. 

  • Early signs of HCM are subtle and may include lethargy, breathing difficulties, and fainting 
  • HCM eventually leads to congestive heart failure and increased risk of blood clots which may trigger severe pain, collapse, and death 
  • Suspicion of HCM may arise when a heart murmur or arrhythmia is detected during a routine wellness exam; diagnosis is confirmed by an echocardiogram
  • HCM has no cure and there is no way to delay its progression   
  • Treatment options exist for heart failure and blood clots, however, both are life-threatening conditions
  • Some cases stabilize and require only ongoing monitoring
  • Medications may provide temporary relief of symptoms associated with heart failure
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A closer look: Heart Disease (Hypertrophic Cardiomyopathy) in Cats

Hypertrophic cardiomyopathy (HCM) is a serious condition in cats with a wide variety of presentations and outcomes. Many cats have stable disease and require no intervention beyond regular monitoring, however, HCM is a common cause of sudden death in cats. Thromboembolism (blood clot) is a complication of HCM which is often fatal. Congestive heart failure is another complication of HCM. Medications often provide temporary relief from symptoms of congestive heart failure, but the long-term prognosis is poor.

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Risk factors

HCM is commonly diagnosed in young to middle aged cats. Many cases have no symptoms, or mild symptoms, such as lethargy and reduced exercise, that are mistaken for aging. Congestive heart failure is a secondary condition to HCM.

In rare cases sudden death occurs. Cats with HCM are predisposed to developing blood clots (thromboembolic disease). If a blood clot lodges in the aorta where it divides to go to the rear limbs (saddle thrombus), symptoms include a sudden onset of rear limb paralysis with vocalization and clear distress.

Cats with symptoms of that present with sudden onset blood clots require immediate treatment for pain relief and blood clots. Many cats with thromboembolic disease are euthanized due to severe pain and poor prognosis. Signs of severe blood clots are a medical emergency requiring immediate veterinary attention.

Possible causes

The cause of HCM is unknown in many cases, however some breeds are predisposed, suggesting a genetic component.

Testing and diagnosis

Many cases of HCM begin with detection of a heart murmur during a routine health examination. Definitive diagnosis involves ultrasound of the heart to demonstrate thickening of the heart muscle. Additional diagnostics include bloodwork and an ECG.

Steps to Recovery

Treatment options vary depending on the severity of the disease and how quickly it progresses. Mild, slowly-progressive HCM without symptoms may not require treatment. There is no treatment that slows the progression of the disease prior to the onset of congestive heart failure.

Once congestive heart failure begins it can be treated with medication that improves symptoms and delays progression temporarily.

HCM is a progressive lifelong condition. Prognosis depends on how quickly the condition leads to congestive heart failure and whether severe blood clots form as the disease progresses.

  • Cats with low grade HCM sometimes never require treatment and the disease is not life limiting.
  • Other cats progress to congestive heart failure and require ongoing medication. Many cats stabilize with treatment but congestive heart failure is usually life limiting.
  • Some cats develop blood clots and sometimes present with sudden death without any other symptoms.
  • Blood clots are a very painful condition and cats require hospitalization and high levels of pain relief while managing the clot. Many cases are humanely euthanized at presentation due to poor prognosis and pain levels.


HCM is not a preventable condition. At-risk breeds can benefit from screening from a young age.

Many cases of HCM have an inherited component and affected cats should not be bred.

Is Heart Disease (Hypertrophic Cardiomyopathy) in Cats common?

HCM is common in cats.

Typical Treatment

  • Treatment of congestive heart failure
  • Treatment of blood clots
  • Pain relief
  • Ongoing monitoring


No Author - Writing for Merck Veterinary Manual
Eliza Smith - Writing for dvm360®
Mark Rishniw, BVSc, PhD, DACVIM (SA-IM), DACVIM (CA) - Writing for Veterinary Partner
No Author - Writing for Cornell University College of Veterinary Medicine
Clarke E. Atkins, DVM, DACVIM (Internal Medicine & Cardiology) - Writing for Veterinary Partner
Vetstream Ltd; Liz Bode BVSc PhD DipECVIM(CA)-Cardiology FHEA FRCVS - Writing for Vetlexicon

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