The protective effects of captopril were evaluated in vitro on isolated perfused rat hearts after a global ischemia of 20 min. The hearts were randomly allocated in 2 groups. In the first one (n = 6) captopril was added at a concentration of 270 microM. The second one was utilized as control (n = 6). Aortic flow and minute work respectively decreased on reperfusion by 35% and 49% in captopril group and by 65% and 71% in controls (p < 0.001). No changes occurred in heart rate. Aortic systolic pressure and coronary flow decreased in the 2 groups, but not significantly. Myocardial enzyme release during reperfusion showed significant lower levels of CPK and LDH in the captopril group as compared to controls (p < 0.001 after 41 min). The occurrence of serious ventricular arrhythmias was considerably higher in controls with respect to the captopril group. Irreversible ventricular fibrillation occurred only in control hearts (50%). These data indicate that captopril exerts a protective effect during myocardial ischemia and reperfusion by preventing serious ventricular arrhythmias, reducing enzymatic release and a lower decrease in cardiac performance, without an increase in heart rate.