Twenty patients who had undergone elective coronary artery bypass grafting were divided into two groups according to the cardiac rhythms after aortic declamping. Eight patients had ventricular fibrillation (Vf group) and 12 patients had spontaneous resumption of heart beating in regular sinus rhythm (SPB group). In Vf group, percent CK-MB and absolute value of CK-MB on the first postoperative day showed significant increase compared with those of the SPB group (p < 0.01). Furthermore, duration of ventricular fibrillation after aortic declamping tended to be positively correlated (r = 0.7018) with absolute value of CK-MB on the first postoperative day, although this did not reach statistic significance (p = 0.0523). To the contrary, between the two groups no significant difference was found in percent LDH1, absolute value of LDH1, and ratio of LDH1 to LDH2 on the first and third postoperative day. It is suggested that ventricular fibrillation after aortic declamping plays a crucial role in increasing postoperative CK-MB level, and its duration is presumably correlated with the absolute value of CK-MB on the first postoperative day.