Abstract: Objective To explore the mechanism of protective effect of vitamin D on cardiovascular tissue in the rats with myocardial infarction.Methods With a pre-experiment,the best time of 1,25 dihydroxyvitamin D3(1,25OH2D3) intervention was determined by observing the expressions of Toll like receptor(TLR4) and its related signaling molecules in A7R5 cells treated with both lipopolysaccharide(LPS) and 1×10^-7 mol/L 1,25(OH)₂D₃.The rats were randomly divided into 2 groups:myocardial infarction(MI) model group(n=16) and 1,25(OH)₂D₃ treatment group(n=16),and a sham-operation group was used as control.The rats in 1,25(OH)₂D₃ treatment group were administered with 1×10^-7 mol/L 1,25(OH)₂D₃ by gavage 48 hours after the MI operation and the rats in other two groups were treated with normal saline;the treatments were performed once a day for 4 weeks.At the end of the treatments,myocardial infarct size(MIS) and cardiac serum enzymes of the rats were detected.The level of TLR4,myeloid differentiation factor 88(MyD88),and nuclear factor kappa-light-chain-enhancer of activated B cells(NF-κB) were detected with real-time PCR and Western blot.Results Vitamin D had inhibitive effect on LPS-induced elevations of TLR4,MyD88 and NF-κB in A7R5 cells(P<0.01).Vitamin D could decrease MIS significantly(P<0.01) and improve the cardiac serum enzymes(P<0.01).Vitamin D could inhibit the expressions of TLR4,MyD88 and NF-κB in myocardial tissue(P<0.01).Conclusion Vitamin D has cardiovascular protective effect through downregulating TLR4 and its relation signaling molecules MyD88 and NF-κB.