Abstract： Objective To investigate whether direct administration of adenoviral vectors (Ad) containi ng the complementary deoxyribonucleic acid (cDNA) of vascular endothelial growth factor 165 (Ad-VEGF165) induces porcine coronary collateral vessel formation, improves regional myocardial perfusion and function and is safe. Methods Three weeks after miniature swine underwent left thoracotomy and placement of an Ameroid constrictor on the left circumflex coronary artery (LCX), Ad-VEGF165 ( n=6) or the control, Ad expressing β-galactosidase cDNA (Ad-Gal, n=6), was di rectly administered into the ischemic myocardium in the circumflex distribution . All animals were sacrificed 4 wk after the second surgery. Myocardial perfus i on and function were assessed by electrocardiogram-gated single photon emission computed tomography (GSPECT) imaging. Ex vivo coronary angiography was perform ed to examine collateral vessels. Toxicity was assessed by blood analyses on th e day just before (day 0) and on day 1, 3, 7, 28 after vector delivery and by va scular, myocardial and liver histology after sacrifice. Results GSPECT imaging 4 wk after administration of Ad-VEGF165 demonstrated significant reduction in ischemic area (P＜0.01) and rest ischemic severity (P＜0 .01) and significant improvement in the left ventricular ejection fraction (P ＜0.01) and regional wall motion (P＜0.05) compared with that of Ad-Gal and before administration of Ad-VEGF165. Collateral vessel development assess ed by coronary angiography was significantly greater in the Ad-VEGF165 group th an in the Ad-Gal group (P＜0.05). General safety parameters, including ro utine blood parameters, liver and kidney function and cardiac specific parameter s demonstrated no difference between Ad-VEGF165 and Ad-Gal animals except for the red blood cell count on day 28 (P＜0.05) and blood urea nitrogen on day 7 (P＜0.05).Only transient elevations in creatine phosphokinase (P＜0 .05) and aspartate transaminase (P＜0.05) on day 1 were revealed compared with that before vector administration in both groups. Histologically, no ather osclerotic lesion in the circumflex and no inflammation in liver were revealed a nd only a small myocardial necrosis was observed in one Ad-VEGF165 animal (area ≤20%) and one Ad-Gal animal (area＜10%). Conclusions Ad-VEGF165 can induce coronary collateral vessel formation, improve regional my ocardial perfusion and function and is safe by means of direct injection, which suggesting that this strategy may be useful in treating human ischemic heart dis ease.