1. The circulating and tissue renin-angiotensin systems (RAS) contribute importantly to cardiovascular homeostasis. Systemic and/or local activation of the RAS is seen in many pathological conditions of the cardiovascular system (e.g. hypertension and congestive heart failure). Increased angiotensin production participates in the pathophysiology of these and other disease states. Accordingly, inhibitors of the renin angiotensin system have a broad spectrum of therapeutic efficacy. 2. Angiotensin-converting enzyme (ACE) inhibitors are effective antihypertensive agents that do not adversely affect serum lipid levels. In addition, they reduce left ventricular hypertrophy. 3. ACE inhibitors cause coronary vasodilation and reduce ventricular work and wall stress. They have been shown to reduce experimental infarct size and to increase anginal threshold in humans. 4. After experimental or human myocardial infarction that results in significant left ventricular dysfunction, ACE inhibitors prevent ventricular dilatation and development of congestive heart failure, and may improve survival. 5. ACE inhibitors can prevent ventricular fibrillation and contractile impairment (stunned myocardium) associated with reperfusion injury after experimental myocardial ischaemia. 6. ACE inhibitors reduce preload and afterload, improve exercise capacity, reduce ventricular arrhythmias, and improve patient survival in clinical cardiac failure. 7. Taken together, inhibition of the RAS may potentially result in primary as well as secondary protective effects on the cardiovascular system.