The renin-angiotensin-aldosterone system plays an important role in the development of congestive heart failure (CHF). In patients with chronic heart failure, angiotensin-converting enzyme (ACE) inhibitors, such as captopril, enalapril, and quinapril, have been shown to improve hemodynamics, reduce symptoms of fatigue and dyspnea, increase exercise capacity, correct hyponatremia, reduce diuretic requirements and ventricular arrhythmias, and conserve potassium and magnesium. ACE inhibitors reduce circulating levels of angiotensin II and aldosterone and may reduce plasma norepinephrine and vasopressin levels. They are equally effective in patients with mild to moderate heart failure and in patients with severe cardiac impairment. ACE inhibitors are at least as beneficial as digitalis in patients with mild heart failure, and they may even be considered as first-line therapy. Promising results have also been obtained in patients with myocardial infarction, in whom long-term therapy with ACE inhibitors has prevented an increase in heart size. ACE inhibitors improve prognosis in patients with severe heart failure and in patients with hyponatremia; the question of effect on survival in mild to moderate heart failure has yet to be answered.