The clinical, hemodynamic and angiocardiographic findings in a group of fourteen patients with idiopathic myocardial hypertrophy are described. These patients were either asymptomatic, or their symptoms showed little if any progression over many years. None had congestive heart failure, cardiac dilatation, arrhythmias or evidence of embolization, features which have been considered characteristic of cardiomyopathies. Instead, the clinical findings of brisk arterial pulses, loud fourth heart sounds, ejection systolic murmurs and evidence of left ventricular hypertrophy on clinical, electrocardiographic, roentgenologic and angiocardiographic examinations were similar to the findings in patients with idiopathic hypertrophic subaortic stenosis. In contrast, however, none of the patients described in this report exhibited any hemodynamic evidence of obstruction to blood flow during the control state.