Following acute myocardial infarction, patients are at increased risk of developing heart failure, which is more prevalent in those with reduced ventricular systolic function. Activation of the renin-angiotensin-aldosterone system, which occurs early after myocardial injury, plays a central role in the pathogenesis of subsequent cardiac structural and functional abnormalities. The early use of angiotensin-converting enzyme inhibitors and angiotensin receptor blockers has been tested in several large randomized clinical trials. The results of these trials show that this treatment strategy reduces the incidence of heart failure and mortality in the postmyocardial infarction patient. The magnitude of benefit is larger in patients with high-risk features, particularly those with large infarct size and the presence of heart failure or left ventricular systolic dysfunction at the time of myocardial injury. Careful use of these agents is essential in avoiding clinically significant hypotension in the critical period.