Abstract: Objective To investigate the effects of ischemic postconditioning on apoptosis and structural and functional changes of mitochondria induced by myocardial isehemia/reperfusion(I/R)injury of rabbits in vivo and potential mechanism. Methods Eighty healthy rabbits were divided randomly into five groups：sham operation group(Group Sham)，ischemic reperfusion group (Group IR)，ischemic preconditioning group (Group IP), ischemic postconditioning group (Group PC)and 5-HD plus ischemic postconditioning group (Group PC+5-HD)，with ten rabbits in each．All rabbits in the five groups were killed 4h after reperfusion．The heart was quickly removed to be used for observing the structure of mitoehondria and measurement of the apoptosis rate by TUNEL. We observed ultrastructural changes of myocardium under electron microscope and examined mitochondrial membrane potential and Ca2+ concentration, MDA content and SOD activity of myocardial mitochondria. Results Compared with group IR,the damage of mitoehondrial ultrastrueture were milder and the apoptosis rate were decreased and Ca2+ concentration and MDA content were much lower in group IP and group PC (P< 0.05)．Mitochondrial membrane potential and SOD activity of myocardial mitochondria in group IP and group PC was significantly higher than that in group IR(P

Key words: isehemia reperfusion, postconditioning, mitochondria, apoptosis