Canis ISSN: 2398-2942

Heart: hypertrophic cardiomyopathy (HCM) and hypertrophic obstructive cardiomyopathy (HOCM)

Contributor(s): Simon Swift, Liz Bode


  • HCM and HOCM are rare diseases.
  • Cause: mild to severe concentric hypertrophy of the left ventricle. HOCM has been associated with hypovolemia, resolving once treated.
  • Signs:: heart failure, sudden death or death under anesthesia.
  • Diagnosis: ultrasonography.
  • Treament: manage heart failure, beta blocking agents (especially HOCM), if present treat hypovolemia.
  • Prognosis: variable, heart failure can be severe. HOCM in young dogs can resolve.



  • Unknown.
  • Idiopathic: important to differentiate from secondary, eg aortic/pulmonic stenosis causes of hypertrophy.
  • Genetic: some families of cats and 50% of human cases are inherited, usually in an autosomal dominance pattern. No information on this in dogs.
  • Hypovolemia: reported in dogs to cause HOCM secondary to hypovolemia induced changes in ventricular geometry.


  • Characterized by an asymmetrically thick left ventricle with a normal to small left ventricular chamber. The increased wall thickness decreases the afterload and results in a stiff chamber.
  • Increase in diastolic intraventricular pressure, left atrial enlargement and eventually congestive heart failure Heart: congestive heart failure. Abnormal papillary muscle orientation and thickening may produce systolic anterior motion of the mitral valve and hence mitral regurgitation.
  • As a result of the increased diastolic intraventricular pressure, the myocardium takes longer to relax in early diastole which can increase diastolic pressure at fast heart rates.
  • Incomplete relaxation of the myocardium. Myocadial fibrosis exacerbates abnormal diastolic function and may worsen with age.
  • The stiff chamber and mitral regurgitation may contribute to left atrial enlargement.
  • Systolic anterior motion (SAM) of the mitral valve - the anterior leaflet of the mitral valve is pulled into the left ventricular outflow tract during systole. In extreme cases it may touch the intraventricular septum obstructing outflow. It is thought that the Venturi effect, whereby a high velocity flow pulls the valve into the flow, contributes to this phenomenon and that the abnormal pull of the papillary muscles also plays a role. In addition the movement of the valve causes significant mitral regurgitation.
  • The decreased end diastolic volume may eventually cause stroke volume to decrease and compromise total body perfusion.


  • Uncertain. Some dogs survive to at least middle age with no clinical signs, but sudden death and congestive heart failure have been reported at a variety of ages.
  • Once heart failure develops, it is usually severe.
  • HOCM in young dogs may spontaneosly resolve with or without beta-blocker therapy.


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Further Reading


Refereed papers

  • Recent references from PubMed and VetMedResource.
  • Hammes K, Novo Matos J, Baron Toaldo M & Glaus T (2016) Hypovolaemia induced systolic anterior motion of the mitral valve in two dogs. J Vet Cardiol 18(4), 367-371 PubMed.
  • Loureiro J, Smith S, Fonfara S, Swift S, James R & Dukes-McEwan J (2008) Canine dynamic left ventricular outflow tract obstruction: assessment of myocardial function and clinical outcome. JSAP 49(11), 578-586 PubMed.
  • Thomas W P et al (1984) Hypertrophic obstructive cardiomyopathy in a dog. Clinical, hemodynamic, angiographic and pathologic studies. JAAHA 20 (2), 253-60 VetMedResource.
  • Liu S K, Maron B J & Tilley L P (1979) Hypertrophic cardiomyopathy in the dog. Am J Path 94 (3), 497-507 PubMed.

Other sources of information

  • Stern J A & Meurs K M (2017) Myocardial disease. In: Textbook of Veterinary Internal Medicine. Ettinger & Feldman (eds). pp 1269-1277.
  • Kittleson M D (1998) Hypertrophic Cardiomyopathy. In: Small Animal Cardiovascular Medicine. Ed: Kittleson & Keene. pp 347-362.