Angiotensin-converting enzyme inhibitor therapy has been shown to be effective in treating patients across the spectrum of cardiac disease. Utility has been demonstrated for both prevention and treatment. This article reviews the data regarding angiotensin-converting enzyme inhibitor therapy in acute myocardial infarction, with emphasis on determining what is known regarding the mode of administration, optimal timing for initiation of treatment, and whether patients can be identified who are most likely to benefit from treatment.