A randomized, double-blind design with single experimental and control groups. Patients were recruited while in the hospital for an acute myocardial infarction and were enrolled in the study before discharge. Eligible patients fulfilled the study definition of an acute myocardial infarction. The diagnosis was based either on electrocardiographic records showing evolving QRS segment changes or on ST segment and T wave changes together with enzyme changes and appropriate clinical history. One-half of the patients were placed on therapy using a beta-blocking drug (propranolol). The other half received a placebo. The prescribed maintenance dosage of propranolol was either l80 or 240 mgs/day, depending upon serum drug levels. Intervention duration averaged 25 months.