BACKGROUND: Apoptosis, as opposed to necrosis, is a active and regulated mode of cell death. Persistent myocardial ischemia results in necrosis. The most effective method to limit ischemic myocardial injury is reperfusion, however, reperfusion itself may be associated with tissue injury. The pathophysiologic findings of myocardial ischemia-reperfusion are well known. However, involvement of apoptosis, as a form of tissue damage, has not neen well defined. Recently apoptosis has been suggested as a specific feature of myocardial reperfusion injury leading to late cell death. This study was performed to investigate whether reperfusion induces apoptosis irrespective of reperfusion time, and the pattern of distribution and the extent of apoptosis in rabbit myocardium. METHOD: New Zealand white rabbits weighing 1.8-2.9kg underwent 20 or 30 minutes left anterior descending(LAD) or left circumflex coronary artery occlusion followed by reperfusion for 30 minutes(n=1), 1 hour(n=1), 3 hours (n=2), and 4 hours (n=3). Ventricles were excised immediately after intervention. Tissues were fixed in 10% buffered formalin and embedded in paraffin. Apoptosis was examined by hematoxylin and eoisin(H & E) staining, in situ nick end labeling, and transmission electron microscopy. Number of apoptotic cells was evaluated semiquantitatively on H & E stained section. Myocardial tissues of ischemia only(LAD occlusion for 30 minutes, n=2) and normal rabbits(n=2) were also examined. RESULTS: Evidence of apoptosis was detected in every ischemia-reperfused myocardium irrespective of reperfusion time of 30 minutes to 4 hours. Apoptotic cells were found in the non-necrotic myocardium near necrotic areas and in islets of the non-necrotic myocarium inside necrotic areas. In the areas where apoptotic cells were distributed, the average number of apoptotic cells ranged from 1.0(30 minutes and 1 hour reperfused myocardium) to 1.1(3 hours and 4 hours reperfused myocardium) per high power field(X400)(the proportion ; less than 1% of cardiomyocytes at specific time point of reperfusion). Apoptotic cells were not detected in ischemia only and normal myocardium. CONCLUSION: These fingings suggest that apoptosis is involved as a form of cell death and it may contribute to cardiomyocyte loss not to a large extent in ischemia-reperfusion injury of rabbit myocardium.