The effects of the long-acting angiotensin-converting enzyme inhibitor benazepril hydrochloride on exercise tolerance and signs and symptoms of congestive heart failure (CHF) were evaluated in a double-blind, multicenter, placebo-controlled clinical trial. Patients with chronic New York Heart Association class II to IV symptoms of CHF and an ejection fraction by radionuclide scanning of less than or equal to 35% were randomized in a 2:1 ratio to treatment with ascending doses of oral benazepril (n = 114) or placebo (n = 58) once daily, while continuing to receive background therapy with digoxin and diuretics. After randomization, patients were evaluated clinically every 2 weeks during a 12-week, double-blind treatment period. Maximal exercise tolerance was measured before and at specified time points after randomization by graded treadmill exercise testing. At week 12, mean exercise time increased 95 +/- 12 (SEM) seconds in the group receiving benazepril, whereas the increase was 37 +/- 18 seconds in the group receiving placebo (p less than 0.01 for the difference between the groups). There was also greater improvement in overall clinical status and in the signs and symptoms of CHF in benazepril-treated patients than in control subjects. There were 3 deaths in placebo-treated patients and none in benazepril-treated patients (p less than 0.05); the overall incidence of adverse effects was identical in the 2 groups. Benazepril is a well-tolerated angiotensin-converting enzyme inhibitor that provides clinically important improvement in exercise tolerance and in signs and symptoms when given once daily to patients with CHF receiving background therapy with digoxin and a diuretic.