We have prospectively studied the prevalence and natural history of left ventricular aneurysm in a series of 386 consecutive male patients with an acute myocardial infarction. Definition of aneurysm was angiographic and based on a single plane left ventricular angiogram. There were 52 (13.5%) left ventricular aneurysms. Mean follow-up was 57 +/- 29 months (range 40-100). During this interval, 15 of the 52 patients died (29%). Univariate analysis showed that survivors had at admission significantly less prevalence of hypercholesterolemia, previous myocardial infarction and intraventricular conduction disturbances. In addition, their Killip class was better (p less than 0.02) and the left ventricular ejection fraction was higher (p less than 0.002). The survival rates of patients with ventricular aneurysm at 1, 3 and 5 years were 88, 82 and 75%, respectively. Left ventricular end diastolic pressure, number of diseased vessels and the presence of bifascicular block were independent predictors of survival. Stratification of patients according to the risk factors allowed identification of patients with excellent prognosis (those with left ventricular end diastolic pressure less than 20 mmHg, single vessel disease and no conduction disturbances) and others with high risk of death (left ventricular end diastolic pressure greater than or equal to 20 mmHg, three vessel disease and bifascicular block). Survival at 5 years for these two groups were 81% vs 50%, respectively (p less than 0.005).