<p><b>BACKGROUND</b>Cell-based vascular therapies of endothelial progenitor cells (EPCs) mediated neovascularization is still a novel but promising approach for the treatment of ischemic disease. The present study was designed to investigate the therapeutic potentials of human umbilical cord blood-derived EPCs (hUCB-EPCs) in rat with acute myocardial infarction.</p><p><b>METHODS</b>Human umbilical cord blood (hUCB) mononuclear cells were isolated using density gradient centrifugation from the fresh human umbilical cord in healthy delivery woman, and cultured in M199 medium for 7 days. The EPCs were identified by double-positive staining with 1, 1'-dioctadecyl-3, 3, 3', 3'-tetramethylindocarbocyanine percholorate-labeled acetylated low-density lipoprotein (Dil-Ac-LDL) and fluorescein isothiocyanate-conjugated Ulex europaeus lectin (FITC-UEA-l). The rat acute myocardial infarction model was established by the ligation of the left anterior descending artery. The hUCB-EPCs were intramyocardially injected into the peri-infarct area. Four weeks later, left ventricular function was assessed by a pressure-volume catheter. The average capillary density (CAD) was evaluated by anti-VIII immunohistochemistry staining to reflect the development of neovascularization at the peri-infarct area. The graft cells were identified by double immunofluorescence staining with human nuclear antigen (HNA) and CD31 antibody, representing human origin of EPCs and vascular endothelium, respectively. Expressions of cytokines, proliferating cell nuclear angigen (PCNA), platelet endothelial cell adhesion molecule (PECAM) and vascular endothelial growth factor (VEGF) were detected to investigate the underlying mechanisms of cell differentiation and revascularization.</p><p><b>RESULTS</b>The donor EPCs were detectable and integrated into the host myocardium as confirmed by double-positive immunofluorescence staining with HNA and CD31. And the anti-VIII staining demonstrated a higher degree of microvessel formation in EPCs transplanted rats, associated with a significant improvement of global heart function in terms of the increase of left ventricular end-systolic pressure (LVESP), +dp/dtmax and -dp/dtmax as well as the decrease of LVEDP in rats with EPCs therapy comparing to the control rats (P < 0.05). Moreover, the expression of the rat PCNA mRNA and PECAM were both enhanced in the EPCs group compared with that of the control group.</p><p><b>CONCLUSIONS</b>The human umbilical cord blood-derived EPCs could incorporate into new-born capillaries in rat myocardium, induce revascularization and improve the proliferation activity in the peri-infarct area, resulting in the improvement of global heart function. This may indicate a promising stem cell resource in cell-based therapy for ischaemic diseases.</p>