The use of angiotensin-converting-enzyme (ACE) inhibitors in patients with heart failure and after myocardial infarction (MI) is discussed, and results of relevant studies are reviewed. In several large trials, the administration of captopril or lisinopril within the first 36 hours after the onset of chest pain due to MI was associated with significant reductions in mortality risk, compared with placebo. Trials evaluating the use of captopril, ramipril, or trandolapril at least three days after the onset of chest pain due to MI also demonstrated significant reductions in mortality risk. Pivotal clinical trials of captopril, enalapril, lisinopril, and ramipril in the treatment of heart failure are presented. Overall, ACE inhibitor therapy was shown to reduce mortality by decreasing the progression of heart failure. Possible benefits of ACE inhibition in addition to reductions in afterload and preload and preservation of serum potassium are discussed. Certain ACE inhibitors may exert positive effects by modulating plasminogen activator inhibitor-1, endothelial function, and left ventricular remodeling. If not contraindicated, long-term therapy with captopril, lisinopril, or ramipril should be used in post-MI patients. Patients with heart failure should be treated with one of the ACE inhibitors that have been shown beneficial for this indication.