BACKGROUND In recent years, there has been a substantial increase in the use of arterial grafts for coronary revascularization. Arterial grafts are more vulnerable than saphenous vein grafts to hypoperfusion syndrome. The purpose of this study was to examine flow competition between the right gastroepiploic artery and native coronary arteries in patients undergoing coronary artery bypass grafting. METHODS Between December 1989 and July 1995, 182 patients underwent coronary artery bypass grafting using the right gastroepiploic artery. Coronary flow patterns were examined in 172 patients by postoperative angiography. Flow patterns were divided into four types: right gastroepiploic artery dependent (n = 128), balanced (n = 24), native dependent (n = 18), or occluded (n = 2). RESULTS All grafts with an old myocardial infarction (n = 75) and 94% of grafts with 99% stenosis (n = 16) were classified in the right gastroepiploic artery-dependent category. In patients with angina pectoris, flow patterns were more frequently classified as right gastroepiploic artery dependent, with increasingly severe native coronary artery proximal stenoses (99% > 90% > 75%) or with stenoses more distal in location. CONCLUSIONS Flow competition depended on three factors: the viability of the revascularized area, the degree of proximal stenosis, and the location of stenosis. Right gastroepiploic artery grafts should be selected for coronary artery bypass grafting with consideration of these three factors.