One hundred patients admitted to the hospital with acute myocardial infarction who lived 10 days and agreed to enroll were studied. Data from the history, hospital course and a 24 hour Holter electrocardiographic recording were related to cardiac mortality in the 6 months after enrollment. Fifteen cardiac deaths occurred during this period; 12 of these were sudden. The univariates with the strongest association with mortality were (in descending order): blood urea nitrogen level, serum creatinine level, serum uric acid level, enlarged heart 2 weeks after infarction, ventricular tachycardia 2 weeks after infarction, peak creatine kinase level and left ventricular failure in the coronary care unit. The odds of dying if one of these factors was present rather than absent ranged from 3.6 to 11.5. Groups with two or these univariates had up to 20 times the odds of dying in 6 months. A period of greately enhanced risk for cardiac death persists for about 6 months after acute myocardial infarction. Relatively simple clinical variables can identify the groups at highest and lowest risk. This information is useful for designing management strategies.