Objective To investigate the effect of L-carnitine injection on oxidative stress and clinical efficacy in patients with acute anterior ST segment elevated myocardial infarction ( STEMI ) and received primary percutaneous coronary intervention .Methods 70 patients with acute anterior wall STEMI undergoing primary PCI in our hospital were randomly divided into the L-carnitine treatment group and the control group.Patients in both groups received same standardized treatment including aspirin , clopidogrel, statins, ACEI/ARB etc.after PCI.Serum levels of superoxied dismutase ( SOD ) and malondialdehyde ( MDA) were measured at arrival and 7 days after PCI.Laboratory results and echocardiography finding were compared.Results (1) The serum SOD levels in both groups were elevated on day 7 after treatment (P<0.05).The serum SOD level on day 7 in the L-carnitine treatment group was higher than the control group (P<0.05).(2) The serum MDA levels in both groups were lower 7 days after treatment (P<0.05).The serum MDA level in the treatment group was lower than the control group (P<0.05).(3) Echocardiography exam on day 7 showed left ventricular end diastolic diameter ( LVEDd) and left ventricular ejection fraction (LVEF) were more significantly improved compared with the control group (P<0.05).Conclusions For AMI patients receiving primary PCI , L-carnitine injection can increase serum SOD concentration and reduce the production of MDA , showing inhibiting effects on oxidative stress and has protective effect on myocardia .