Abstract: Objective Observing the effects of ischemic postconditioning on ischemia/reperfusion injury in rat heart in vitro and reseaerching the mechanisms elementarily. Methods The wistar rat hearts were put in the Langendorff equipment, and the myocardial ischemia/reperfusion and the ischemic postconditioning model in vitro were made. Observing the changes of maximal rate of the pressure increase and decrease (±dp/dtmax) , and left ventricular end diastolic press（LVEDP）of heart. Colorimetry method was used to assay the lactate dehydrogenase (LDH) of fluid, methy lnedioxyamphetamine (MDA) and superoxide dismutase (SOD) activity of cardiac muscle; western blotting method was used to detect endothelial nitric oxide synthase (eNOS) and phosphorylated extracellular-regulated kinases (ERK1/2) expression；RT-PCR method was used to test CYP2J3 mRNA expression of heart. Results Compared with group IR, the value of ±dp/dtmax was increased（P<0.01）, LVEDP and LDH level was decreased（P<0.05） in group IPo in reperfusion stage. The content of MDA in group IR was higher than in group CON and IPo（P<0.01）. The activity of SOD in group IR was lower than IPo（P<0.01）, but it was almost equal to group CON .The expression of eNOS and phosphorylated ERK1/2 in group IR was higher not only than group CON but also than IPo. The CYP2J3 mRNA expression of heart in group IPo was evidently higher than group CON and IR. Conclusions Ischemic postconditioning can improve the myocardial dysfunction and cell injury caused by ischemia/reperfusion in rat heart in vitro, maybe through activation of SOD and increasing elimination of oxygen-derived free radicals. CYP2J3/EET system involved in protective effection probably.