Cardioprotection due to angiotensin enzyme inhibitors is attributed, at least in part, to the inhibition of bradykinin breakdown and the preconditioning effect of the elevated endogenous bradykinin level. We have previously shown that in patients undergoing percutaneous coronary intervention, one 120-second balloon inflation is insufficient to precondition the heart. The objective of the present study was to examine whether the administration of enalaprilat to these patients results in protection. Twenty patients underwent two 120-second coronary artery occlusions separated by a reperfusion interval of 10 min. Ten patients were given 50 microg x min-1 enalaprilat in an intracoronary infusion between the balloon inflations, whereas the others received an infusion of saline. In the latter control patients, there were no significant differences in ST-segment elevation between the consecutive occlusions (peak ST: 1.61 +/- 0.17 vs. 1.61 +/- 0.16 mV; time to reach 0.5 mV ST elevation: 16 +/- 4 vs. 22 +/- 7 s; mean ST: 1.03 +/- 0.12 vs. 1.02 +/- 0.11 mV). In the patients who received enalaprilat before the second balloon inflation, the ST-segment elevation was significantly less pronounced and slower during the second inflation than during the first (peak ST: 1.80 +/- 0.18 vs. 1.41 +/- 0.19 mV; time to reach 0.5 mV ST elevation: 18 +/- 4 vs. 30 +/- 4 s; mean ST: 1.04 +/- 0.11 vs. 0.85 +/- 0.14 mV). We conclude that enalaprilat administered during percutaneous coronary intervention provides protection to patients who do not have a protective response to the initial balloon inflation.