Objective To investigate the effect of combined therapy of granulocyte colony stimulating factor (G-CSF) and bone marrow mesenchymal stem cells (BMSCs) carrying hepatocyte growth factor (HGF) gene on the angiogenesis of myocardial infarction (MI) in rats and the mechanisms of the synergistic effect. Methods BMSCs were aspirated from the femur and tibia of 3-week-old Sprague Dawley (SD) male rats. The third generation of BMSCs were harvested and transfectedwith Ad-HGF. The MI models were establ ished in 44 SD male rats (weighing 200-250 g) by l igating the left coronary artery. At 4 weeks after l igation, the shorting fraction (FS) of the left ventricle being below 30% was used as a criteria of model success. The BMSCs (5 × 107/ mL) transfected with Ad-HGF were transplanted into the infarct zone of 12 SD rats, and the expression of HGF protein was detected by Western blot method at 2, 7, and 14 days after transplantation. At 4 weeks, the other 32 SD rats were randomly divided into 4 groups (n=8). The 0.1 mL normal sal ine was injected into the infarct zone in control group; 0.1 mL normal sal ine was injected combined with intraperitoneal injection G-CSF [100 μg/ (kg•d)] for 5 days in G-CSF group; 0.1 mL BMSCs (5 × 107/ mL) transfected with Ad-HGF was injected into the infarct zone in HGF group; 0.1 mL BMSCs (5 × 107/ mL) transfected with Ad-HGF was injected combined with intraperitoneal injection G-CSF [100 μg/ (kg•d)] for 5 days in combined therapy group. At 2 weeks after transplantation, heart function was detected by cardiac ultrasound and hemodynamic analysis, and then myocardial tissue was harvested to analyse the angiogenesis of the infarct zone, and the expression of VEGF protein by immunofluorescence staining. Results The expression of HGF protein in vivo was detected at 2 days and 7 days of BMSCs transfected with Ad-HGF transplantation. There was no significant difference in left ventricular systol ic pressure (LVSP), left ventricular end-diastol ic pressure (LVEDP), dP/dtmax, and FS between G-CSF group and control group (P gt; 0.05). When compared with the control group, LVEDP decreased significantly; LVSP, FS, and dP/dtmax increased significantly (P lt; 0.05) in HGF group and combined therapy group. When compared with HGF group, FS and dP/dtmax increased significantly in combined therapy group (P lt; 0.05). Immunofluorescence staining showed that the vascular endothel ial cells were observed in myocardial infarction border zone. The vascular density and the expression of VEGF protein were significantly higher in combined therapygroup than in other 3 groups (P lt; 0.05). Conclusion The combined therapy of G-CSF and BMSCs carrying HGF gene has a synergistic effect and can enhance infarct zone angiogenesis through inducing the expression of VEGF protein.