Left ventricular function was studied in 15 patients with rapidly progressive Duchenne de Boulogne muscular dystrophy. Only one patient had a previous history of cardiac failure. All patients had typical electrocardiographical changes. Haemodynamic and angiographic investigation was performed in all patients. Three groups of patients were distinguished according to angiographic criteria : group I comprising 7 normal patients. group II comprising 4 "intermediary" patients, and group III of 4 patients with hypokinetic cardiomyopathy. Segmental ventricular dyskinesis was observed in 6 patients. Mitral incompetence was present in 2 cases and mitral valve prolpse in 1 case. All patients had a normal resting cardiac index. Patients in group II and III had end diastolic left ventricular pressures greater than 15 mmHg. An intravenous angiotensin test was performed in 4 patients from groups I and II. Impaired left ventricular function was demonstrated in patients thought to be normal in the basal state. Finally, myocardial involvement in this group of patients runs a parallel course to the duration and severity of the peripheral muscular disease.