Background: Circulating endothelial progenitor cells (EPCs) are known to be involved in vasculogenesis and mobilized after acute myocardial infarction (AMI). We investigated the relation between the EPC mobilization and improvement of left ventricular (LV) function and predictor for EPC mobilization. Methods: We enrolled 36 patients with LV ejection fraction (EF) < 50% who underwent percutaneous coronary intervention (PCI) for AMI. The number of EPC and the levels of serum vascular endothelial growth factor (VEGF), macrophage chemoattractant protein (MCP-1), and interleukin-10 (IL-10) were measured in the peripheral blood before PCI and after 5days of PCI. The follow-up LVEF was measured at 6 months after PCI. According to the mobilization of EPC, patients were divided into 2 groups [group I: mobilized group (n=18), group II: non-mobilized group (n=18)]. Results: Baseline CD45lowCD34+VEGFR2+ cells were significantly higher in the group II than in the group I (63.9짹95.7 vs. 213.7짹235.8/106 leukocyte, p=0.023). The change of CD45lowCD34+VEGFR2+ cells were significantly higher in the group I than the group II (319.2짹525.4 vs. -161.7짹212.3/106 leukocyte, p=0.001). The group I had lower N-terminal pro-B-type natriuretic peptide (NT-proBNP) levels than the group II (1641.0짹3026.5 vs. 1829.7짹1470.7 pg/mL, p=0.039, respectively). The baseline levels of VEGF, MCP-1, and IL-10 were no significant differences. The level of VEGF increased significantly at 5 day after PCI in the group I but not the group II (5.2 pg/mL to 12.0 pg/mL, p=0.035 in the group I, 6.7 pg/mL to 11.7 pg/mL, p=0.052 in the group II). The baseline LVEF was similar between the groups (41.9짹6.7 vs. 41.4짹7.3 %, p=0.546). At 6-month after PCI, the LVEF was improved significantly in Group I (39.1 % to 51.5%, p<0.001). In multivariate analysis, baseline NT-proBNP level and ��VEGF (VEGF at 5 day minus baseline VEGF) were associated with EPC mobilization (OR, 13.36, 95% CI 1.43-124.23, p=0.001; OR, 6.00, 95% CI 1.15-31.22, p=0.033, respectively) and mobilization of EPC was an independent predictor of LV functional improvement (OR, 1.98; 95% CI 1.02 to 3.43, p=0.036). Conclusion: The EPC mobilization after PCI in patients with AMI was related to improvement of LVEF. The baseline NT-proBNP and ��VEGF were independent predictors of EPC mobilization in patients with AMI treated with PCI.