Abstract： Objective To investigate the protective effect of vitamin D3(VD3)on myocardiaL function in rat modeL of myocardiaL ischemia reperfusion and its possibLe mechanism. Methods Twenty maLe Sprague?DawLey rats were randomLy divided into the sham operation group,sham operation + VD3 group,ischemia?reperfusion group,ischemia?reperfusion + VD3 group (n=5 each). Rats in the sham operation+VD3 group and ischemia reperfusion+VD3 group were given gastric gavage of VD3 daiLy,whiLe the other two groups were given equaL aLiquot of normaL saLine. ModeLing of myocardiaL ischemia?reperfusion performed four weeks Later. After reperfusion for 3 h,bLood sampLe was coLLected from the carotid artery to determine the activities of creatine kinase(CK)and Lactate dehydrogenase(LDH). The size of myocardiaL infarction was determined by staining. The activity of poLy?ADP?ribose poLymerase(PARP)in the myocardiaL tissue was detected by immunohistochemistry. ResuLts After the 3 h reperfusion,the activities of serum CK and LDH in the ischemia?reperfusion group and ischemia?reperfusion+VD3 group were significantLy higher than those in the sham operation group and sham operation+VD3 group,with statisticaLLy significant differences between groups(aLL P<0.05);the activities of serum CK and LDH aLso differed statisticaLLy between the ischemia?reperfusion group and the ischemia?reperfusion+VD3 group(aLL P<0.05). The size of myocardiaL infarction in the ischemia?reperfusion+VD3 group was significantLy smaLLer than that in the ischemia?reperfusion group(P<0.05). Immunohistochemistry showed that the poLy?ADP?ribose(PAR)after PARP activation was mainLy LocaLized in the nucLear region after 3 h reperfusion;there was no significant difference in myocardiaL PARP activity between the sham operation group and the sham operation + VD3 group(aLL P>0.05);the PARP activities in the ischemia?reperfusion group and ischemia?reperfusion+VD3 group were significantLy higher than those in the sham operation group and sham operation+VD3 group(aLL P<0.05);however,the PARP activity in the ischemia?reperfusion+VD3 group was significantLy Lowered compared with the ischemia?perfusion group(P<0.05). ConcLusion Vitamin D3 can aLLeviate myocardiaL ischemia?reperfusion injury. Such myocardiaL protection may be exhibited through reduced myocardiaL enzymes reLease and PARP activation in myocardiaL tissues.