AIM:To investigate the effect of hypericin(Hyp)on the heart of rats with myocardial ischemia-re-perfusion injury(MIRI),and to explore its mechanism.METHODS:Thirty SPF male SD rats were divided into 5 groups:sham group,MIRI group,low-dose Hyp(L-Hyp)group(MIRI+L-Hyp group),high-dose Hyp(H-Hyp)group(MIRI+H-Hyp group),and positive control trimetazidine(TMZ)group(MIRI+TMZ group),with 6 rats in each group.Apart from the sham group,the MIRI model was established by ligating the anterior descending branch of the left coronary artery and then recanalizing it in the remaining four groups of rats.The success of the modeling was determined by monitor-ing the electrocardiogram.We assessed the cardiac function in rats using echocardiography.TTC staining was employed to measure the area of myocardial infarction in rats,and HE staining was utilized to observe the morphological traits of rat myocardium.We assayed the activities of lactate dehydrogenase(LDH)and superoxide dismutase(SOD)and the levels of malondialdehyde(MDA)in rat serum using biochemical kits.ELISA kits were applied to assess the contents of cardiac troponin I(cTnI)and reactive oxygen species(ROS)in rat serum.Western blot analysis was perfomed to measure the pro-tein expression levels of AMPK,p-AMPK,Nrf2,and HO-1 in rat myocardial tissues.RESULTS:The rats in MIRI group exhibited increased myocardial tissue injury,larger myocardial infarction areas,decreased left ventricular ejection fraction(LVEF),and reduced left ventricular fractional shortening(LVFS)compared with sham group,as shown by echo-cardiography.Additionally,there were increases in LDH activity,cTnI,MDA and ROS levels,along with significant de-creases in SOD activity,and p-AMPK,Nrf2 and HO-1 protein levels(P<0.05).Compared with MIRI group,the rats in MIRI+L-Hyp,MIRI+H-Hyp and MIRI+TMZ groups showed decreased myocardial histopathological damage and reduced myocardial tissue infarction area,increased LVEF and LVFS,and lowered serum levels of LDH activity,cTnI,MDA and ROS,while SOD activity,p-AMPK,Nrf2 and HO-1 protein levels were elevated(P<0.05).CONCLUSION:Hypericin attenuates myocardial ischemia-reperfusion injury in rats,possibly by modulating the AMPK/Nrf2/HO-1 signaling path-way.