Progressive enlargement following myocardial infarction can be anticipated to adversely effect outcome since prognosis is intimately related to the degree of left ventricular dysfunction and resultant ventricular cavity size. Recent experimental and clinical data have indicated that chronic angiotensin converting enzyme inhibitor therapy can be effective in attenuating the ventricular enlargement which occurs following infarction. These observations have provided a rationale for ongoing large multicenter clinical trials designed to determine whether angiotensin converting enzyme inhibition will be of clinical benefit following infarction. This article reviews the rationale for studies of angiotensin converting enzyme inhibition in post-infarct patients and summarizes the ongoing international research effort to fully define the role of angiotensin converting enzyme inhibition following infarction.