We investigated the protective effect of angiotensin II (Ang II) type 1 receptor antagonist on myocardial ischemia-reperfusion injury and the role of exogenous Ang II to this injury in perfused hearts. We orally administered TCV-116 (Ang II type 1 receptor antagonist) and delapril (angiotesin converting enzyme inhibitor) to Wistar rats for 1 week and measured the immunoreactive cardiac Ang II. Immunoreactive cardiac Ang II (pg/gm tissue) was 14.3 ± 2.0 in control group, 11.8 ± 0.8 in TCV-116-treated group, and 7.3 ± 0.6 in delapril-treated group (p < 0.05) compared to TCV-116-treated group; p < 0.01 compared to control group). The 15 hearts (five rats in each group) were perfused by a Langendorff method and global ischemia was maintained for 30 min. Both TCV-116 and delapril were found to improve postischemic cardiac function and decrease reperfusion creatine kinase (CK) release. Ang II injection before ischemia worsened postischemic cardiac function and increased reperfusion CK release. Only TCV-116 prevented this injury. These data indicated that TCV-116 Ang II type 1 receptor antagonist was effective against myocardial ischemia-reperfusion injury, and exogenous Ang II accerelated this injury through Ang II type 1 receptor.