In patients with acute ST-segment elevation myocardial infarction (STEMI), percutaneous coronary intervention (PCI) may cause thrombus dislodgment and impaired microcirculatory reperfusion. This study was designed to test the hypothesis that thrombus aspiration before standard PCI may improve acute myocardial reperfusion, measured by ST-segment resolution (STR) and myocardial blush grade (MBG), compared with standard PCI.