Background: No-reflow or slow flow is an important phenomenon to limit the patients��� prognosis after primary angioplasty in patients with acute myocardial infarction (AMI). Coronary stenting is a current standard procedure of primary angioplasty in AMI. But stenting is suspected to cause more microembolization and slow. We performed this study to elucidate the predictors for no-reflow phenomenon after primary angioplasty with stenting in patients with AMI and to suggest indications to use distal protection device. Methods and Results: Clinical, angiographic and procedure related parameters were reviewed in patients with first AMI who underwent primary angioplasty with stent implantation within 12h after the onset of chest pain. Patients with prior surgical or percutaneous revascularization, primary angioplasty after thrombolysis, left main disease, a definite distal dissection or embolism and the use of distal protection device were excluded and 183 patients were finally enrolled in this study. Twenty-four patients showed no-reflow phenomenon (final TIMI flow grade less than 3). Conventional risk factors for coronary artery disease were not significant risk factors. But, patients with initial CK-MB level more than 50IU (8.45% vs 21.9%, p=0.04), LV EF less than 50% (19% vs 5%, p=0.03), predilatation balloon inflation time more than 30sec (31% vs 15%, p=0.04) and no-reflow after predilatation (39% vs 9%, p<0.01) were significant predictors for no-reflow phenomenon. Degree of calcification, extent of disease, thrombus score and diameter of stent were not significant risk factors of no-reflow phenomenon. All of these predictors except balloon inflation time were also significant in multivariate analysis. The 6 month adverse event (death, MI, target lesion revascularization) rates in patients with no-reflow were not different from the patients with normal flow. Conclusions: High initial CKMB level, LV dysfunction and and post-balloon no-reflow were independent predictors for no-reflow phenomenon after primary angioplasty with stent in AMI. Preventive measures against no-reflow phenomenon including distal protection devices and GpIIbIIIa inhibitors should be considered in the patients with these predictors.