Abstract:Objective：To observe the protective effect of Injection of Panax quinquefolium diolsaponins（IPQDS）and its mechanism on acute myocardial infarction in rats. Method：The acute myocardial infarct model was prepared by left anterior descending coronary occulusion for 24 hours in openchest anesthetized rats. The myocardial infarct size (MIS) was calculated. The activities of serum creatine hosphokinase(CK), lactate dehydrogenase(LDH), aspartate aminotransferase (AST), superoxide dismutase(SOD) and glutathione peroxidase(GSH-Px), and the contents of malondialdehyde (MDA) and nitric oxide(NO) were determined. Blood was collected to observe low shearing specific viscosity, middle shearing specific viscosity and high shearing specific viscosity of whole blood and plasma viscosity. At the same time, the platelet aggregation rate and platelet adherence rate were also determined. Result: In rats treated by IPQDS (in a dosage of 12.5, 25 and 50 mg·kg-1 d, ip 3d ), the MIS was significantly reduced. The activities of serum CK, LDH and AST, and the content of serum MDA were declined. The activities of SOD and GSH-Px, and the content of NO were increased markedly. In addition, low shearing specific viscosity, middle shearing specific viscosity and high shearing specific viscosity of whole blood and plasma viscosity as well as platelet aggregation rate were also declined significantly. But platelet adherence rate had no significant change. Conclusion: IPQDS has a protective effect on acute myocardial ischemia, which may be related to increasing activity of antioxidase in body, scavenging the damage of peroxidation from oxygen free radicals, decreasing the viscosity of blood and plasma and preventting thrombosis etc.