Cloricromene (Clo) has been used to prevent myocardial damage after transient occlusion of the circumflex coronary artery (Cx). Twenty rabbits were injected for 4 days with a single dose of Clo (0.25 mg/kg i.v.) or placebo. On the 5th day, the Cx was occluded, and Clo (6.4 µg/kg/min) or placebo was continuously infused. After 50 min, the occlusion was removed and after 20 min of reperfusion, the rabbits were sacrificed. In the placebo group, all rabbits showed marked ST segment changes and severe ischemic arrhythmias (6/10 animals). In 5 of them, ventricular fibrillation was followed by death. In the Clo group smaller ST segment elevations were observed, and in 2 rabbits ventricular fibrillation spontaneously reversed as did ST segment elevations. A significant reduction of the necrotic area was also observed in the Clo group by postmortem examination.