Hypertrophic Cardiomyopathy

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Left ventricular concentric hypertrophy without an identifiable cause is known as hypertrophic cardiomyopathy. The ventricular myocardium becomes so thick that the lumen is reduced to a size that is not compatible with maintaining the heart's function as a pump. The left ventricle no longer has the capacity to hold normal volumes of blood during diastole. As a result, the left atrium dilates from the increased pressure and volume of blood backing up into the lungs.


This heart disease is rare in dogs but is the most common cardiac disease in cats. It more frequently occurs in Persians and Siamese breeds of cat. It is thought to be inherited in Maine Coon cats.

Clinical Signs

The disease can often be present without clinical signs (asymptomatic).

There may be hindlimb paresis or weakness, if saddle thrombus (cats) occurs due to this disease.

There will usually be signs of left-sided heart failure. Tachycardia, arrhythmias and dyspnoea can also be seen.


Physical examination and auscultation will reveal a systolic murmur and ventricular arrhythmias.

Radiography of the thorax will show a degree of left atrial enlargement, a generally enlarged heart and pulmonary congestion & edema.

On Electrocardiography (ECG), there will often be presence of a tall R wave and a wide QRS complex. Ventricular arrhythmias, conduction disturbances and sinus tachycardia may also be seen.

Upon Echocardiography, left ventricular concentric hypertrophy, left atrial enlargement and mitral valve insufficiency are commonly seen with this condition. The chamber size will appear dramatically reduced.


It is necessary to treat the individual symptoms, as there is no treatment for the condition.

Drugs with contraindications include arterial vasodilators and positive inotropes.


Poor for symptomatic cats.

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Ettinger, S.J. and Feldman, E. C. (2000) Textbook of Veterinary Internal Medicine Diseases of the Dog and Cat Volume 2 (Fifth Edition) W.B. Saunders Company

Ettinger, S.J, Feldman, E.C. (2005) Textbook of Veterinary Internal Medicine (6th edition, volume 2) W.B. Saunders Company

Fossum, T. W. et. al. (2007) Small Animal Surgery (Third Edition) Mosby Elsevier

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