Unusual cardiac manifestations in a patient with myotonic muscular dystrophy.

We report on a patient with myotonic muscular dystrophy in whom mitral valve prolapse associated with prolonged PR interval and left anterior hemiblock was documented 3 years before any clinical evidence of myotonia, muscle weakness or wasting. One year after diagnosis had been established, he developed atrial flutter with 1:1 atrioventricular conduction, an arrhythmia that in addition to complete heart block and ventricular arrhythmias may account for the occurrence of syncope and sudden death in this group of patients.