The Studies of Left Ventricular Dysfunction (SOLVD) examined the effect of an angiotensin-converting enzyme (ACE) inhibitor, enalapril on mortality and hospitalization in 6,797 patients with low ejection fraction (EF < 0.35). Patients requiring treatment for heart failure were entered to the treatment trial (n = 2,569) while those patients not receiving pharmacological treatment for heart failure were entered in the prevention trial (n = 4,228). In the treatment trial, there was a 16% (95% confidence interval [CI], 5% to 26%) reduction in mortality with the largest reduction in deaths due to progressive heart failure (22%, 95% CI, 6 to 35%). There was also a 26% (95% CI, 18 to 34%) reduction in mortality or hospitalization for worsening heart failure. In the prevention trial there was an 8% (95% CI, -8 to 21%) reduction in mortality, 12% (95% CI, -3 to 26%) reduction in cardiovascular mortality, and a 29% (95% CI, 21 to 36%) reduction in mortality or development of heart failure. In addition, there was a 20% (95% CI, 9 to 30%) reduction in mortality or hospitalization for heart failure. There were consistent effects among subgroups defined by baseline serum sodium, vasodilator use, etiology and NYHA functional class. The effect of enalapril on mortality and hospitalization for heart failure was significantly greater for patients with the lowest ejection fraction. In both trials, there were highly significant reductions in myocardial infarction (23%, 95% CI, 11 to 34%) and hospitalizations for unstable angina (20%, 95% CI, 9 to 29%).