The occurrence and importance of nonfatal cardiac events in the year after an acute myocardial infarction were studied in 866 patients who were enrolled by nine hospitals with a broad geographic distribution. The extensive clinical data acquired on each patient included special tests, such as radionuclide-determined ejection fraction, 24 hour ambulatory electrocardiogram and a low level exercise tolerance test. Recurrent events were frequent in the first 5 months, and certain events were significant indicators of a poor prognosis. An ejection fraction less than 40% and angina after discharge from the coronary care unit predicted patients at high risk of rehospitalization. Recurrent infarction was similarly predicted by angina, but not by any features of an exercise test. This study demonstrates the considerable morbidity that occurs after an acute myocardial infarction and its relation to and role in subsequent mortality.