A large number of studies have reported that following CABG, the vessels proximal to the grafts demonstrate accelerated atherosclerosis and the grafts themselves may show progressive obstruction due to thrombosis, fibrosis, and graft atheroma. Pathological and clinical studies have documented that graft obstruction during the perioperative period and the first year is usually due to technical problems at surgery or thrombosis and occurs in about 15 to 20 percent of saphenous vein grafts. Antiplatelet drugs such as aspirin have been shown to reduce these early graft occlusions by about 50 percent. In addition to thrombosis, during the first year, most saphenous vein grafts undergo diffuse fibrosis and some distortion. However, the significance of these changes is not known.