Objective:To investigate the protective effects and its protective mechanism of Magnesium tanshinone ⅡA sulfonate(MTS) on acute myocardial infarction.Methods:The acute myocardial infarction model in rats were performed by the ligation of the left coronaryartery and the successful models were randomly assigned to either a control group(5% glucose solutions) sodium tanshinone ⅡA sulfonate(STS)group(5 mg/kg)

combined MTS group(1

5

15 mg/kg).The corresponding dosages medicine were given to that rats 5 minutes after ligationing through the vena caudalis;The myocardial infarct size

change of enzymes in myocardium and serum were simultaneously monitered 4 hours later.Results:Comparing with control group it was found that MTS decreased the lactic acid dehydrogenase(LDH) and creatine phosphokinase(CK)activity in serum

reduced myocardial infarct size

and improved the activity of superoxide dismutase(SOD) and decreased the malondiadehyde(MDA)contents in myocardium respectively.Conclusion:MTS had protective effects on the acute myocardial infarction by the ligation

the mechanism of the protective effect may be related to its role against oxygen free radical.