Double internal mammary-coronary artery bypass in 100 patients with angina was associated with 35 single-vein grafts and four double-vein grafts. Hospital mortality was 8%. Postoperative catheterization revealed patency of 80 of 84 (95%) right internal mammary artery (RIMA) grafts, 82 of 84 (97%) left internal mammary artery (LIMA) grafts, and 36 of 41(88%) vein grafts. At one year, 22 of 23 (96%) RIMA grafts and 22 of 22 LIMA grafts remained patent. There were two late deaths, one late infarction, and three of 23 patients with angina at one year. Five of 45 IMA grafts had diffuse narrowing. The right and left IMA are hemodynamically similar, but the right will usually not reach beyond the acute margin and is smaller than the right coronary artery (RCA) one third of the time. The LIMA graft is the graft of choice for left anterior descending (LAD) reconstruction, but use of the RIMA for RCA or LAD bypass must be based on the age of the patient, the size of the coronary artery, and the distribution of atherosclerosis.