In order to study the cardioprotective effects of diazoxide on the myocardial ischemia/reperfusion injury of rats and mechanisms, the healthy SD rats were randomly divided into 2groups: the rats in the experimental group were injected with diazoxide for preconditioning with the dosage of 12.5 mg/kg through the right femoral vein and those in the control group was only administered with the equal volume of media. After 10 min, a left thoracotomy was performed and the left anterior descending branch was occluded for 2 h. Two h later, the left anterior descending branch was reperfused for 2 h and then the heart was quickly excised to be used for measurement of MDA, SOD and the infarct size, in situ cell apoptosis detection and observation of the cell ultrastructure by electron microscopy. The results showed that as compared with the control group, MDA, the infarct size and cell apoptosis in the experimental group were greatly reduced (P＜0.05). And the cell ultrastructure was obviously improved. But the activity of SOD had no change (P＞0.05). It was concluded that diazoxide could protect the rats from myocardial ischemia/reperfusion injury, which might be contributed to the reduction of lipid peroxidation and cell apoptosis.