Experiment with recirculating blood perfusion device showed that nicorandil 0.15 mmol/L significantly counteracted the harmful effect of ischemic and reperfused injury on the respiratory function of myocardial mitochondria. The oxidative phosphorylation efficiency (ADP/O) was increased 19% (p less than 0.01), the respiratory control rate(RCR) was also increased 40% (p less than 0.01); while the content of myocardial calcium and Ca/Mg were decreased; and the ischemia and reperfusion-induced increase of myocardial water content was abolished as compared with solvent control. The results indicate that nicorandil has protective effect on myocardial mitochondria function during ischemia and reperfusion, which may be the result of blocking Ca2+ from entering the cell and prevent lipid peroxidation.