Abstract： Background Low molecular weight heparin (LMWH) was more effective than unfractionated heparin (UFH)in treating acute coronary syndrome (ACS). However, it remains uncertain whether LMWH can be used in patients undergoing percutaneous coronary intervention (PCI) instead of UFH. This study aimed to evaluate the efficacy and safety of using enoxaparin instead of UFH in the intervention treatment of patients with coronary heart disease (CHD)Methods From October 2003 to Febuary 2005, 966 patients with CHD were enrolled into this study. Among 966 patients, 455 patients received the PCI, including 283 patients with Non-ST segment elevation ACS (NSTEACS), 511 patients did not received PCI due to mild, moderate lesions or were suitable for coronary artery bypass graft (CABG). The 966 patients were randomized to enoxaparin group (484 patients) and UFH group (482patients). Patients in the enoxaparin group were given enoxaparin at least twice subcutaneously (1 mg/kg, q12 h)before catheterization. Plasma anti-Xa activity was determined 1-8 hours after the last dose of enoxaparin was determined. The catheterization was performed within 8 hours after the last dose of enoxaparin. The sheath was removed immediately after the procedure. Patients in the UFH group were given UFH 25 mg intravenously before coronary angiography. Additional 65 mg was given intravenously if PCI was to be performed. The sheath was removed 4 hours after the procedure.Results A total of 227 patients in the enoxaparin group and 228 patients in the UFH group received PCI. In the enoxaparin group, one patient developed acute thrombosis during PCI and resulted in acute myocardial infarction (AMI), no acute or subacute thrombosis was found during hospitalization. In the UFH group, no acute or subacute thrombosis occurred during PCI procedure and hospitalization. Therefore, the incidence of major adverse cardiovascular events (MACEs) during the hospitalization was 0.44% in the enoxaparin group and 0 in the UFH group. In the enoxaparin group, the sheath was removed immediately after the procedure and 8 patients had hematoma on the puncture site. In the UFH group, the sheath was removed 4 hours after the procedure and 20 cases had hematoma on the puncture site. The incidence of hematoma on the puncture site was significantly higher in the UFH group than that in the enoxaparin group (P＜0.05). Anti-Xa activity was determined in 174 patients in LMWH group. The mean anti-Xa activity was (0.87±0.23) U/ml, and 94.8% of them had anti-Xa activity ＞0.5 U/ml and 6.9% of the patient ＞1.2 U/ml. There was no death and AMI occurred in enoxaparin group,but one patient had AMI caused by subacute thrombosis in UFH group during 30-day follow-up. MACE rate at 30-day follow-up was 0 in enoxaparin group and 0.43% in UFH group.Conclusions The results of the study suggest that it is safe and efficient to give enoxaparin at least twice before the PCI procedure, and the sheath can be removed immediately after PCI. For NSTEACS patient who has received enoxaparin more than twice during the hospitalization can undergo PCI directly and no UFH is necessary before or during PCI.