The effects of angiotensin converting enzyme (ACE) inhibitors on mortality following acute myocardial infarction (MI) has recently been studied in several clinical trials. The rationale for the use of these drugs following an injury to the myocardium is largely based on their ability to attenuate left ventricular volume expansion and modulate neurohormonal activation. Left ventricular dilatation following MI is due to complex structural changes in the infarcted myocardium as well as alterations in the non-infarcted contractile myocardium. The magnitude of this remodelling is associated with adverse prognosis. Neurohormonal systems are activated in the early phase of acute MI. Prolonged neurohormonal activation mainly occurs among patients with marked left ventricular dysfunction. The CONSENSUS II trial examined the effects on mortality of the ACE inhibitor enalapril, when initiated within 24 h from the onset of the infarct and continued for 6 months. There were 6090 patients randomly assigned to placebo (n = 3046) or enalapril (n = 3044). At the end of the trial, 598 patients had died: 286 (9.4%) in the placebo group and 312 (10.2%) in the enalapril group (P = 0.26). These results are in contrast to some other studies in which mortality was reduced by ACE inhibitor therapy post-MI. It is considered likely that the positive effects of ACE inhibitors following MI are confined mainly to patients with marked left ventricular dysfunction and prolonged neurohormonal activation.