This study was performed to examine whether cilazapril, a novel nonsulfhydril angiotensin-converting enzyme (ACE) inhibitor, may improve regional myocardial perfusion at exercise in patients with coronary heart disease (CHD). In a single-blind, nonrandomized trial, 5 mg cilazapril or placebo was administered to eight patients with documented CHD and stable exertional angina. Multistage bicycle exercise tests were performed and each patient served as his own control. At peak exercise, as well as at rest, [99mTc]hexakis-2-methoxy-2-isobutylisonitrile myocardial images were obtained. Percent myocardial activity differences (%AD) between exercise and resting images were compared (cilazapril versus placebo). Heart rate and blood pressure were not significantly different between trials. However, after cilazapril administration, %AD was higher than after placebo, with relative differences between trials of greater than 30%, along with alleviation of clinical symptoms in seven of eight patients. These data suggest that in patients with stable-effort angina, ACE inhibition with cilazapril is able to redistribute myocardial blood flow and to improve regional oxygen supply to the ischemic myocardium.