The effects of the intravenous administration of the angiotensin converting enzyme inhibitor benazeprilat on left ventricular function were examined in 18 patients with ischemic heart disease. Twenty minutes after drug infusion (0.3-10 mg), heart rate (78 +/- 17 to 71 +/- 16 beats/min, p less than 0.0003), left ventricular systolic pressure (-9 mm Hg, p less than 0.0004), and plasma norepinephrine concentration all decreased significantly. The isovolumic indexes of inotropic state also decreased slightly (-10% in dP/dtmax, p less than 0.001), whereas the ejection fraction (39 +/- 16% to 41 +/- 16%, p less than 0.08) and the end-systolic volume (-6%, p less than 0.04) tended to improve, probably because of the afterload reduction (-13% in mean systolic wall stress, p less than 0.05). After benazeprilat administration, the left ventricular end-diastolic pressure was unchanged at the group level, but there was a consistent downward shift of the diastolic pressure-volume relation during rapid filling, and the mean diastolic wall stress decreased from 99 +/- 73 to 69 +/- 42 kdyne/cm2 (p less than 0.007). These data indicate that the acute administration of benazeprilat has a dual action on left ventricular pump function, which is that the negative inotropic effect of bradycardia and reduced sympathetic drive are compensated by afterload reduction. The drug also improved left ventricular diastolic distensibility and significantly reduced wall stress during diastole. The beneficial effects on diastolic function were noted both in patients with mild left ventricular dysfunction and in patients with heart failure.