Preventive therapy by angiotensin-converting-enzyme (ACE) inhibitors is considered in hypertension and, more recently, in chronic heart failure. The mechanism of action of ACE-inhibitors is complex; most extensively studied, however, is their inhibitory effect on angiotensin-II production. ACE-inhibitors may act as vasodilators, reducing pre- and afterload. On the other hand, local renin-angiotensin systems may control growth processes both in myocardial and in smooth muscle cells. This may be another site of action for ACE-inhibitors. ACE-inhibitors are reliable antihypertensive drugs and may have additional specific effects on the heart and vascular smooth muscle. Clear evidence is, however, missing for their superiority above other drugs in preventing cardiovascular complications of hypertension. Most recently, the data of the "study of left-ventricular dysfunction" (SOLVD) and "survival and ventricular enlargement" (SAVE) study became available. These studies showed that ACE-inhibitors could prevent the incidence of heart failure in about one-third of patients with severe left-ventricular dysfunction during 3 years of observation when compared with placebo treated patients. A new indication, therefore, for ACE-inhibitors could be left ventricular dysfunction after myocardial infarction. It remains unclear 1) what could be the adequate diagnostic procedures to identify patients for preventive treatment, 2) when therapy should be started, 3) about the duration of therapy, 4) about the doses of ACE-inhibitors for this indication, 5) what will be the side-effects when used in a broader population, and 6) will this prevention of heart failure be a specific effect of ACE-inhibitors?