After eligible patients are randomized into Planned Staged-dose Group and Planned Single-dose Group, first-dose anticoagulation will be administered immediately. All patients in the Planned Staged-dose Group will receive enoxaparin 0.5 mg/kg at the beginning of coronary angiography and only those with definite indication for subsequent PCI will be given additional enoxaparin 0.25 mg/kg at the beginning of PCI; while, all patients in the Planned Single-dose Group will receive enoxaparin 0.75 mg/kg at the beginning of coronary angiography irrespective of their indication for subsequent PCI. Blood samples for the measurement of Anti-Xa activity will be obtained at 0 min (immediately before first-dose administration), 10 min, 90 min, 180 min after first-dose administration in all patients. Additional blood samples for Anti-Xa assessment will be collected only in patients undergoing subsequent PCI immediately before and at 10 min after the beginning of PCI, as well as at the end of PCI. The primary objective of the present study is to obtain the values of Anti-Xa activity at the above time points in each group of patients. In patients who undergo subsequent PCI, the proportion of patients with therapeutic anticoagulation (Anti-Xa 0.5-1.8 IU/ml) at 10 min after the beginning of PCI and at 90 min after first-dose administration will be compared respectively between the two groups (Staged-dose PCI Group [0.5+0.25 mg/kg] versus Single-dose PCI Group [0.75 mg/kg]). In patients who do not undergo subsequent PCI, the proportion of patients with therapeutic anticoagulation at 10 min and 90 min after first-dose administration will be compared respectively between the two groups (High-dose Group [0.75 mg/kg] versus Standard-dose Group [0.5 mg/kg]).