This multicenter, double-blind, placebo-controlled study compares the effects of captopril treatment with those of digoxin treatment during maintenance diuretic therapy in patients with mild to moderate heart failure. Compared with placebo, captopril therapy resulted in significantly improved exercise time (mean increase, 82 s vs 35 s) and improved New York Heart Association class (41% vs 22%), but digoxin therapy did not. Digoxin treatment increased ejection fraction (4.4% increase) compared with captopril therapy (1.8% increase) and placebo (0.9% increase). The number of ventricular premature beats decreased 45% in the captopril group and increased 4% in the digoxin group in patients with more than ten ventricular premature beats per hour. Treatment failures, increased requirements for diuretic therapy, and hospitalizations were significantly more frequent in patients receiving placebo compared with those receiving either active drug. Transitory hypotension occurred more frequently with administration of captopril. Captopril treatment is significantly more effective than placebo and is an alternative to digoxin therapy in patients with mild to moderate heart failure who are receiving diuretic maintenance therapy.