Background: Large thrombotic burden in STEMI is considered high risk because of its high potential for distal thromboembolism and subsequent microvascular injury. Manual thrombus aspiration (TA) can effectively improve coronary reperfusion for such cases. However, whether successful TA results in early myocardial reperfusion has been unknown. Methods: A total of 98 STEMI patients undergoing primary PCI in our center from Jul, 2007 to May 2009 were evaluated. TA was performed using Thrombuster II (Kaneka Corp. Japan) on infarct related artery (IRA) of diameter ���2.5 mm with initial TIMI flow grade 0-1 or large visible thrombus. Blood CK-MB level was sampled on admission, 6, 12, 24, 36, and 48 hours after primary PCI to measure the peak value and the time to reach it. TIMI flow, TMP grade, and MACE (cardiac death, MI, target lesion revascularization) were assessed. Results: TA was performed in 72 (73%) based on the angiographic selection criteria. There were no significant differences in baseline characteristics, including pain-to-door and door-to-balloon time between TA (n=72) vs. no-TA (n=25) groups. Although TA group had significantly worse initial TIMI flow (grade 0-1: 81% vs. 36%, p<0.001), final TIMI flow (grade 3: 93% vs. 88%, p=0.42), TMP (grade 3: 60% vs. 64%, p=0.91), and MACE at 12 months (10% vs. 8%, p=1.00) were comparable with no-TA group. Peak CK-MB level was significantly higher (257짹174 vs. 177짹157 mg/dL, p=0.045) and the time to reach it was significantly reduced (<6hr: 57% vs. 35%, >12hr: 17% vs. 35%, p=0.032) in TA group. Conclusion: TA achieves the higher and earlier peak CK-MB level suggesting early myocardial reperfusion, and shows comparable final angiographic and clinical outcomes overcoming the worse initial angiographic findings in primary PCI for STEMI. Further imaging or functional study to assess the benefit of early reperfusion achieved by TA will be necessary.