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Heart: hypertrophic cardiomyopathy (HCM)


Synonym(s): HCM


  • Cause: unknown. Heritable in Maine Coon, Ragdolls, and probably Persians and Sphynx cats.
  • Signs: sudden onset in apparently well cat, acute dyspnea, lethargy or signs of thromboembolism.
  • Diagnosis: biomarkers, ultrasound, radiography, ECG.
  • Treatment: diuresis, vasodilators, beta-blockers (in certain cases of HOCM and not when decompensated heart failure).
  • Prognosis: variable.
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  • Two forms of HCM occur:
    • Primary:
      • Largely unknown in idiopathic form.
      • Ragdoll (R820W) and Maine Coon (A31P) can have inheritable form associated with myosin binding protein C.
      • Other inherited predispositions likely as in humans.
      • Oversensitivity to circulating catecholamines may be involved.


  • Characterized by hypertrophied non-dilated left ventricle.
  • Left ventricular diastolic dysfunction   →   decreased distensibility of myocardium   →   increase in end-diastolic pressure with normal or reduced volume.
  • Increased muscle mass, myocardial fibrosis, disordered arrangement of myofibrils   →   decreased distensibility.
  • Abnormal myocardial relaxation   →   prolonged relaxation period and decreased rate of decline of left ventricular pressure.
  • Decreased capillary density in myocardium, abnormally narrowed intramural coronary arteries, increased resistance in large coronary arteries due to systolic pressures   →   myocardial ischemia.
  • Myocardial ischemia   →   abnormal relaxation, increased left ventricular filling pressures.
  • May be mild hypertrophy with severe left heart failure - probably due to abnormal myocyte function.
  • Systolic anterior motion of the mitral valve (SAM) might be present due to abnormal mitral valve apparatus/papillary muscle geometry resulting in hypertrophic obstructive cardiomyopathy (HOCM).

Systemic thromboembolism

  • Turbulence   →   damages cardiac endothelium   →   endocardial collagen induces platelet adhesion and aggregation, extrinsic pathway activation Hemostatic disorders: acquired.
  • Circulation of blood through heart is abnormal   →   areas of sluggish flow allow aggregation of platelets.
  • Higher levels of serotonin in felines due to larger platelets than dogs and humans, felines more sensitive to effects of serotonin   →   higher susceptibility to aggregation.


  • Onset can appear rapid.
  • Survival can be months to years.


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Further Reading


Refereed papers

  • Recent references from PubMed and VetMedResource.
  • Luis Fuentes, V, Abbott, J, Chetboul, V et al (2020) ACVIM consensus statement guidelines for the classification, diagnosis, and management of cardiomyopathies in cats. J Vet Intern Med 34, 1062-1077 PubMed.  
  • Fox P R, Keene B W, Lamb K et al (2018) International collaborative study to assess cardiovascular risk and evaluate long-term health in cats with preclinical hypertrophic cardiomyopathy and apparently healthy cats: The REVEAL Study. J Vet Intern Med 32 (3), 930-943 PubMed.  
  • Cote E (2017) Feline congestive heart failure: Current diagnosis and management. Vet Clin North Am Small Anim Pract 47 (5), 1055-1064 PubMed.
  • Luis Fuentes V, Wilkie L J (2017) Asymptomative hypertrophic cardiomyopathy: Diagnosis and therapy. Vet Clin North Am Small Anim Pract 47 (5), 1041-1054 PubMed.
  • Hogan DF, Fox P R, Jacob K et al (2015) Secondary prevention of cardiogenic arterial thromboembolism in the cat: The double-blind, randomized, positive-controlled feline arterial thromboembolism; clopidogrel vs. aspirin trial (FAT CAT). J Vet Cardiol Supplement 1: S306-317 PubMed.
  • Koffas H, Dukes-McEwan J, Corcoran B M et al (2006) Pulsed tissue Doppler imaging in normal cats and cats with hypertrophic cardiomyopathy. J Vet Intern Med 20 (1), 65-77 PubMed.
  • Connolly D J, Cannata J, Boswood A et al (2003) Cardiac troponin I in cats with hypertrophic cardiomyopathy. J Feline Med Surg (4), 209-216 PubMed.
  • Kraus M S, Calvert C A & Jacobs G J (1999) Hypertrophic cardiomyopathy in a litter of five mixed breed cats. JAAHA 35 (4), 293-296 PubMed.
  • Rush J E, Freeman L M, Brown D J et al (1998) The use of enalapril in the treatment of feline hypertrophic cardiomyopathy. JAAHA 34 (1), 38-41 PubMed.

Other sources of information

  • Chetboul V (2017) Feline myocardial diseases. In: Textbook of Veterinary Internal Medicine. Ed. Ettinger & Feldman. pp 1278-1305.

Related Images


Heart: cardiomegaly

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