Hypertrophic cardiomyopathy associated with myotonic muscular dystrophy (Steinert's disease).

A 52-year-old man with myotonic dystrophy and first degree atrioventricular block, right bundle branch block and left anterior hemiblock was shown by echocardiographic examination to have hypertrophy of the posterior segment of the septum and of the anterior left ventricular wall. Myocardial involvement in this patient may represent the full expression of a genetic defect involving both skeletal and myocardial striated tissue.