Background Attempts to improve late results of bypass coronary surgery have focused on the use of arterial conduits because of the high attrition rate of venous grafts.Methods and Results In our institution, 150 patients received an inferior epigastric artery (EPIG) as a free bypass graft, anastomosed to the right coronary artery in 73% and to a marginal branch in 20% of cases.These patients were followed prospectively by qualitative and quantitative angiography. Angiographic studies were performed in 122 patients (81%) early after surgery (11+-5 days), and in 72 cases, a late evaluation (11+-6 months) was also obtained. Quantitative angiography (basal and after isosorbide dinitrate (ISDN)) was performed on the in situ EPIG in a large subset of these patients, as well as in 59 patients before bypass surgery. The patency rate was 98% at early control and remained high (93%) at late control. However, at late control, 14 EPIGs were occluded or threadlike, but of these 14, eight were grafted on a coronary artery with a moderate stenosis (<=60%) and with good anterograde perfusion. Mean basal EPIG diameter increased from 2.23+-0.42 mm before surgery to 2.57+-0.52 mm at 11 days (P<.01) but decreased to 2.20+-0.47 mm in late study (P<.01 versus 11 days and P=NS versus before surgery). Vasodilation of EPIG with ISDN was observed before surgery (+0.34+-0.20 mm, P<.001) and at late control (+0.20+-0.17 mm, P<.001) but not in the early postoperative period for the whole group. Early after surgery, basal diameter was not different from native EPIG dimensions after ISDN (2.57+-0.52 versus 2.56+-0.39 mm), suggesting maximal dilation. However, vasodilation with ISDN was observed in a subgroup of patients at this time. These responder patients (n=51) had a smaller basal diameter (2.47+-0.49 versus 2.67+-0.54 mm, P<.05) and a smaller runoff (P<.001) than nonresponder patients.Conclusions EPIG grafts have a good early patency rate.The mid-term patency rate remains high and seems to depend, at least partially, on flow through the native coronary artery. EPIGs initially increase their lumen size, probably to meet the increased blood flow due to myocardial requirements. Over time, EPIG diameters decrease mainly as a result of a higher basal vasomotor tone. Long-term angiographic follow-up (eg, 5 to 10 years) is needed to assess late patency rate and the rela tion with these early findings and will define the place of this new coronary bypass conduit. (Circulation. 1994;90(part 2):II-148-II-154.)