Objectives: Graft stenosis is a major complication of coronary artery bypass grafting with autologous saphenous vein grafts. Nitric oxide (NO) is believed to prevent this phenomenon. We studied the effect of perivascular application of an NO donor on the degree of stenosis of such grafts in an ovine model., Methods: Twenty white Iranian ewes were randomized to coronary artery bypass grafting using autologous saphenous vein grafts with application of an elastomer gel containing diethylenetriamine NO adduct in 0.9% sodium chloride solution around the grafted vessel (intervention group) or with the gel containing the saline solution alone (controls). Graft vessels were studied after 1 year using spot angiography and histological examination., Results: The mean degree of stenosis was significantly lower in the intervention group than in the controls as found by histology (92.3 ± 5.5 vs. 80.9 ± 8.3%; p = 0.004). Although the difference in the angiographic score was not significant, the mean score was still lower in the intervention group (9.5 ± 11.3 vs. 12.0 ± 11.8)., Conclusions: Perivascular application of an NO donor was, at least histologically, effective in reducing graft stenosis in our ovine model. This can be a step toward the development of drug-eluting coronary artery bypass grafts., (Copyright © 2011 S. Karger AG, Basel.)