Objective To probe into impacts of safflor yellow injection on rats with acute myocardial infarction and discuss its mechanism. Methods Forty Sprague-Dawley rats were divided into sham operation group ( 8 rats ) and operation groups(32 rats).The left anterior descending branch of coronary artery was ligated to establish an animal model with acute myocardial infarction.The rats with successful modeling were randomly divided into model control group, 3-, 7- and 14-days safflor yellow group.In the treatment group, the rats were injected with safflor yellow injection(2.5 mg.kg-1.d-1)for 3, 7 and 14 days, respectively.Rats in sham operation and model control group were injected 0.9% sodium chloride solution.Their weights were measured 24 h after the last drug administration, their hearts were removed, and the serum was obtained through centrifugation.The enzymic method was used to measure the lactate dehydrogenase(LDH)and creatine kinase(CK)contents of serum.Hematoxylin eosiny(HE)staining method was used to observe the change of myocardial cells.The chloride three phenyl-tetrazole( TTC) staining method was used to measure the area of myocardial infarction in the rats. The real-time fluorescent quantitative PCR method was used to measure the expression of VEGF and HIF mRNA at the marginal zone of myocardial infarction. Results The levels of LDH and CK were(106.12±35.52),(452.84±60.38)mmol.L-1 in sham operation group, and(385.66±137.58),(2 111.00±1 250.80)mmol.L-1 in model control group.LDH in 3-, 7-, 14-days treatment groups was (249.66±51.86),(104.33±51.08),(110.33±26.76)mmol.L-1, while CK was(1 713.00±584.74),(1 177.66±980.18), (421.33±54.60)mmol.L-1.LDH and CK levels of the 14-days treatment group were significantly lower than those in the model control group(both P<0.05).The area of myocardial infarction was (0.00±0.00)% in sham operation group,(13.12±6.69)% in the model control group, and(8.11±3.45)%,(7.01±2.98)%,(3.44±1.17)% in the 3-, 7-, 14-days treatment groups.The area of myocardial infarction in the 14-days treatment group was significantly lower than that of the model control group(P<0.05).The expression of VEGF and HIF mRNA was 1.99±0.27, 6.21±1.35 in the sham operation group, 1.03±0.15, 1.78±0.57 in the model control group.The expression of HIF mRNA in the 3-, 7-, 14-days treatment groups was 0.50±0.12, 1.23±0.24, 2.20± 0.32, and the expression of VEGF mRNA in the 3-, 7-, 14-days treatment groups was 0.43±1.27, 2.67±0.83, 5.78±1.23. Conclusion The safflor yellow injection has therapeutical effects on the rats with acute myocardial infarction, and the effects will become significant after 14 day.It can reduce the area of myocardial infarction and LDH and CK content at the drug administration groups, which might be related to the increase of the expression of VEGF and HIF mRNA.