Heart Disease (Hypertrophic Cardiomyopathy) in Dogs

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Last updated on
4 min read

Key takeaways

Hypertrophic cardiomyopathy (HCM) is a rare form of heart disease in dogs which results in enlargement of the heart muscles.

  • Excessive enlargement narrows the internal size of the heart chambers, reducing blood flow
  • HCM is usually affects young dogs under 3 years old, and often has no symptoms
  • Many dogs are diagnosed when a heart murmur is detected during routine physical examination
  • HCM progresses over time and results in congestive heart failure (CHF)
  • Other symptoms relate to the onset of CHF and include exercise intolerance, difficulty breathing, weight loss, and coughing
  • Diagnostics include physical examination, blood work, and diagnostic imaging, including electrocardiogram
  • Treatment involves multiple medications to address specific aspects of the condition
  • Most cases respond well to treatment with improvement of symptoms, but many cases result in euthanasia due to an ultimately poor prognosis
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A closer look: Heart Disease (Hypertrophic Cardiomyopathy) in Dogs

HCM is a serious condition seen primarily in young dogs. The initial presentation varies in severity from acute collapse or sudden death, to detection of a heart murmur with no other symptoms on routine physical examination.

HCM is a progressive condition. Medication slows progression and improves symptoms, but ultimately, HCM is a life-shortening condition in young dogs.

Dogs presenting with acute collapse require emergency veterinary attention. Young dogs found to have a heart murmur require urgent investigation.

HCM presents in two forms.

Acute onset describes the severe onset in an otherwise healthy dog, and results from sudden increased demand for cardiac output, such as during strenuous exercise or a sudden drop in blood pressure.

Symptoms include:

  • Collapse during activity or exercise
  • Sudden death
  • Death under anesthesia

Chronic onset results from the gradual progression of HCM which reduces cardiac output over time, resulting in congestive heart failure.

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Risk factors

Most cases show no symptoms initially.

All symptoms of heart failure are an emergency requiring immediate veterinary attention.

Since HCM is not well understood in dogs, it is not clear if there are any predisposing factors at this time.

Possible causes

The disease process of HCM is not fully understood in dogs. It is a common disease in cats and has shown to be a genetic disease in this species. There may be an inherited component in dogs that has not yet been identified.

Main symptoms

Testing and diagnosis

Further investigation of HCM involves:

  • Physical examination
  • X-rays
  • Echocardiography
  • Electrocardiogram (ECG)
  • Blood pressure monitoring

Steps to Recovery

Treatment options depend on the severity of onset, but normally requires a variety of medication. Medications selected for treatment aim to:

  • Reduce fluid accumulation in the chest and abdomen
  • Improve efficiency of the heart muscle
  • Slow heart rate to improve filling of the heart

HCM sometimes presents as sudden death. Other cases result in congestive heart failure over time, and are life-shortening for the patient. In most cases, treatment is effective at improving symptoms and extending life. Dogs that develop congestive heart failure are typically euthanized due to a poor prognosis, often at a young age.


Prevention is not possible, as the underlying disease process is not fully understood. HCM may be a heritable disease and affected animals should not be bred.

Is Heart Disease (Hypertrophic Cardiomyopathy) in Dogs common?

HCM is rare in dogs.

Typical Treatment

  • Medication
  • Supportive care
  • Palliative care


No Author - Writing for Merck Veterinary Manual
Mark Rishniw, BVSc, PhD, DACVIM (SA-IM), DACVIM (CA) - Writing for Veterinary Partner
Mark Rishniw, BVSc, PhD, DACVIM (SA-IM), DACVIM (CA) - Writing for Veterinary Partner
Simon Swift MA VetMB CertSAC DipECVIM-CA MRCVS, Liz Bode BVSc PhD DipECVIM(CA)-Cardiology FHEA FRCVS - Writing for Vetlexicon

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