Illustration of a longitudinal section through the human heart in hypertrophic cardiomyopathy, showing massive enlargement of the muscular septum separating the left and right ventricles (bottom left on image). The term cardiomyopathy describes a heart muscle disease of unknown cause: hypertrophy refers to the increase in size of the heart muscle brought about by the enlargement of its cells rather than by cell multiplication (as occurs, for example, in normal growth and tumour formation).