The objective of this study was to evaluate the use of an angioscope-assisted laser hot-tip probe for performing valvulotomies in in situ nonreversed canine veins used for arterial bypasses. In Group 1, 9 valvulotomies were performed in 7 bypass veins with a 2-mm probe activated by 12 W power, resulting in 4 vein perforations, 1 vein thrombosis, and 4 in situ grafts patent at removal after 2-28 days. In Group 2, 10 valvulotomies in 9 bypass veins were performed with a 1.5-mm probe at 14 W with no vein perforations, 3 vein thromboses, and 6 in situ grafts patent at removal after an interval of 1 to 6 weeks. We conclude that valvulotomy within in situ vein bypasses can be successfully performed using a 1.5-mm laser hot-tip probe at 14 W power, with patency of the grafts demonstrated at 6 weeks. Angioscope-assisted laser valvulotomy using a laser probe may significantly reduce the length of incisions and the time required for in situ vein bypasses and improve the technical accuracy of the procedure.