Objective To investigate the effects of nicorandil (Nic) pretreatment on myocardial apoptosis in a rabbit model of myocardial ischemia/reperfusion (I/R) .Methods Forty healthy male New Zealand white rabbits aged 4 months weighing 2.0-2.5 kg were randomly allocated to one of 5 groups ( n = 8 each); group 1 sham operation; group 2 I/R; group 3 Nic; group 4 Nic + 5-hydroxydecanoic acid (5-HD) and group 5 Nic + glibenclamide (Gli) . The animals were anesthetized with IV pentobarbital 30 mg?kg-1 and tracheotomized and breathing spontaneously. A piece of thread was placed around the circumflex branch of left coronary artery, which was reversibly occluded for 30 min and released for 120 min reperfusion. In group 3, 4 and 5 a loading dose of 100 ?g?kg-1 Nic was given IV 10 min before myocardial ischemia followed by Nic infusion at 10 ?g?kg-1 ?min-1 until myocardial ischemia was started. In group 4 and S 5-HD 5 mg? kg-1 or Gli 5 mg? kg-1 was given IV 20 min before ischemia. At the end of 120 min reperfusion the animals were killed and the hearts removed. The area of myocardial infarct (AI), and the ischemic risk zone (AR) were determined by computer morphometry. The early apoptotic myocytes were detected by flow cytometry (Beckman, Coulter Co). The expression of caspase-3 protein was determined by immuno-histochemistry. The myocardial ultrastructure was examined with transmission electron microscope.Results Compared to group 2 (I/R) , in nicorandil group (group 3) the size of myocardial infarct and the number of early apoptotic cells were significantly reduced, the ultrastructure of myocardium was well-preserved and the expression of activated caspase-3 protein decreased. The protective effect of Nic preconditioning was greatly inhibited by 5-HD and Gli pretreatment. Conclusion Nicorandil pretreatment exerts protective effect against myocardial I/R injury through activation of mito-KATP C and inhibition of activation of caspase-3.