Left ventricular dilation and dysfunction after myocardial infarction are major predictors of death. In experimental and clinical studies, long-term therapy with captopril, an angiotension-converting enzyme inhibitor, decreased ventricular dilation and rearrangement. This study was undertaken to examine whether captopril may reduce morbidity and mortality in patients with left ventricular dysfunction following myocardial infarction. On days 3 to 16 after myocardial infarction, 2231 patients with <40% ejection fraction, but without signs of obvious heart failure ot symptoms of myocardial ischemia were studied in a double-blind study, of them 1116 took placebo and 1115 had captopril. The follow-up averaged 42 months. The mortabity due to any causes was significantly lower in the captopril group (228 deaths or 20% than in the placebo group (275 deaths or 25%). The decrease in the risk was 19 percent (95 percent confidence interval, 3 to 32 percent; p = 0.019). The incidence of fatal and grave nonfatal cardiovascular events significantly decreased in captopril-treated patients. The risk decrease was 21 percent (95 percent confidence interval, 5 to 35 percent; p = 0.014) for cardiovascular mortality; 37 percent (95 percent confidence interval, 20 to 50 percent; p < 0.001) for the development of severe heart failure; 22 percent (95 percent confidence, 4 to 37 percent, p = 0.019) for congestive heart failure requiring hospitalization; 25 percent (95 percent confidence interval, 5 to 40 percent; p = 0.015) for recurrent myocardial infarction. Thus, long-term captopril use in patients with asymptomatic left ventricular dysfunction following prior myocardial infarction resulted in survival improvement and decreased morbidity and mortality due to severe cardiovascular events. There were positive results both in patients treated with thrombolytics, aspirin or <$Ebeta>-blockers and in those untreated with the above drugs. This suggests that the use of captopril additionally improved the therapeutic outcomes in patients with prior myocardial infection.