The EPPAC (Etude de la perméabilité des pontages aortocoronaires) is a randomised prospective (18 centres) double blind trial designed to compare the patency of coronary bypass grafts in two groups of coronary patients after surgery: one group treated with oral vitamin-K antagonists and placebo (n = 196, age 57 +/- 5 years, 2.09 grafts/patient) and the other group with vitamin-K antagonists and dipyridamole (n = 182, age 56 +/- 6 years, 1.99 grafts/patient), the principal criterion of evaluation being the patency of the grafts at coronary angiography performed 6 months after surgery, interpreted by two independent observers. Of the 469 patients included (average ejection fraction 59.5 +/- 2.2%), 378 underwent the control coronary angiography at the 6th month and 773 saphenous vein grafts were evaluated. At the end of the study, there were 12 deaths, 10 due to perioperative myocardial infarction, and 24 nonlethal myocardial infarctions. The frequency of occlusion of at least one graft per patient was 18.2%, the patency of the graft at the distal anastomosis was 89.9%. The following factors played a major role: the cardiological center: the occlusion rate per patient ranged from 7.1 to 57.1% and per anastomosis from 2.8 to 28.6%; the internal diameter of the artery grafted: when 2 mm or more, the occlusion rate was 17.6% compared with 42.3% (p less than 0.001); the technique used for distal anastomosis: 9.2% of grafts with single outflow sites occluded, compared with 4.3% of grafts with multiple outflow sites. Early occlusion of saphenous vein aorto-coronary grafts is the main problem of this form of therapy and the addition of dipyridamole to oral anticoagulants does not seem to reinforce the anti-thrombotic effect at 6 months after surgery.