A totol of 50 SD rats were randomly divided into sham operation group， model group， low dose （20 mg·kg^－1） of crocin group， medium dose （40 mg·kg^－1）of crocin group and high dose （80 mg·kg^－1） of crocin group， with 10 rats in each group. The myocardial ischemia reperfusion injury rat models were established by ligation of left anterior descending coronary artery and reperfusion. The morphology of myocardium tissue of rats in various groups was observed by HE staining. TUNEL was used to detect the apoptosis of myocardial cells， and the apoptotic index （AI） was calculated. The expression levels of B-cell lymphoma-2（Bcl-2）， Bcl-2 associated X protein（Bax） and caspase-3 mRNA and proteins in myocardium tissue of the rats were determined by RT-PCR and Western blotting methods. The levels of malondialdehyde （MDA） and the activities of superoxide dismutase （SOD）， lactate dehydrogenase （LDH）， and creatine kinase （CK） in myocardium tissue of the rats in various groups were detected with detection kits.

The myocardial fibers of the rats in sham operation group were arranged neatly； the myocardial fibers of the rats in model group were disordered， edema occurred， and the inflammatory cells were abundant in myocardial stroma；compared with model group， the inflammation and infiltration of the rats in low dose of crocin group were significantly reduced， and the myocardial fiber edema was significantly reduced； there was no significant edema of myocardial fibers with little inflammatory infiltration in medium and high doses of crocin groups. Compared with sham operation group， the AI of myocardium of the rats in model group was increased （P<0.05），the expression levels of Bcl-2 mRNA and protein in myocardium tissue of the rats in model group were significantly decreased （P<0.05）， the expression levels of Bax and caspase-3 mRNA and proteins were significantly increased （P<0.05）， the serum MDA level was significantly increased （P<0.05），the SOD activity was significantly decreased （P<0.05）， and the LDH and CK activities were significantly increased （P<0.05）. Compared with model group， the AI of myocardium of the rats in low， medium and high doses of crocin groups were significantly decreased （P<0.05），the expression levels of Bcl-2 mRNA and protein in myocardium tissue of the rats were significantly increased （P<0.05）， the expression levels of Bax and caspase-3 mRNA and protein were significantly decreased（P<0.05）， the serum MDA levels were significantly decreased （P<0.05）， the SOD activities were significantly increased （P<0.05），and the LDH and CK activities were significantly decreased （P<0.05）. Compared with low dose of crocin group， the AI of myocardium of the rats in medium and high doses of crocin groups were significantly decreased（P<0.05）， the expression levels of Bcl-2 mRNA and protein in myocardium tissue were significantly increased （P<0.05）， the expression levels of Bax and caspase-3 mRNA and proteins were significantly decreased（P<0.05）， and the MDA levels and the activities of SOD， LDH and CK in serum had no significant differences（P>0.05）. Compared with medium dose of crocin group， the expression levels of Bcl-2 mRNA and protein in myocardial tissue were significantly increased （P<0.05），the expression levels of Bax and caspase-3 mRNA and proteins were significantly decreased（P<0.05）， the AI of myocardium of the rats in high dose of crocin group was significantly decreased （P<0.05）， and the MDA level and the activities of SOD，LDH and CK in serum had no significant differences（P>0.05）.

Different doses of crocin have protective effects on myocardial injury caused by ischemia and hypoxia in a dose-dependent manner， and its mechanism may be related to reducing the apoptosis of myocardial cells， and relieving myocardial oxidative stress injury.