We tested the hypothesis that, in the acute phase of ST-segment elevation myocardial infarction (STEMI), the circulating level of P-selectin (PS) is predictive of angiographic morphologic features that indicate burden of thrombus formation in the infarct-related artery (IRA). One hundred and ninety-five consecutive patients with acute myocardial infarction (AMI) who underwent primary percutaneous coronary intervention (PCI) within 12 h of symptom onset were divided into the high-burden thrombus formation (HBTF) (N = 84) group and low-burden thrombus formation (LBTF) group (N = 111) based on cineangiography carried out during PCI. Blood samples for measurement of the circulating levels of high-sensitive C-reactive protein (hs-CRP), interleukin-6 (IL-6), soluble intercellular cell adhesion molecule-1 (sICAM-1), PS and white blood cell (WBC) count were collected before PCI. The WBC count, neutrophil granulocyte count and PS level were significantly higher in the HBTF group than in the LBTF group (11.24 +/- 3.62 vs 10.00 +/- 3.35, p = 0.014; 8.84 +/- 3.42 vs 7.66 +/- 3.23, p = 0.015; 13.62 +/- 8.13 vs 7.80 +/- 4.17, p = 0.000, respectively). Patients in the HBTF group had a significantly lower prevalence of post-PCI thrombolysis in myocardial infarction (TIMI) grade-3 flow than that of the LBTF group (84.52% vs 93.69%, p = 0.037). Compared with the LBTF group, the HBTF group had higher peak values of the myocardial band (MB) fraction of creatine kinase (CK-MB). (308.52 +/- 215.26 vs 213.79 +/- 185.27, p = 0.005). By logistic regression analysis, PS (OR 1.259, 95% CI 1.125 - 1.408, p = 0.000) were independent predictors of thrombus formation. PS level was the strongest independent predictor of angiographic morphologic features that indicate HBTF in AMI.