Eight hundred fourteen patients with internal mammary artery (IMA) coronary artery bypass grafts have been restudied 961 times with coronary arteriography, primarily to evaluate the patency of the grafts in the setting of symptomatic coronary occlusive disease. Their records were reviewed to assess graft patency as related to the technical aspects of coronary artery bypass surgery. Patency was evaluated using life-table analysis of the data. The method of harvesting the IMA played no role in patency. The left anterior descending coronary artery was the recipient coronary artery with the highest patency rate. The left IMA had a significantly higher patency rate than the right IMA. As a group, the IMAs had a significantly higher patency rate than saphenous vein grafts. However, there was no difference between right IMA grafts and saphenous vein grafts. The mammary artery grafts that remained patent throughout the study had a significantly higher blood flow after bypass than did those that became occluded (43.0 +/- 0.9 versus 28.9 +/- 1.8 ml/min; p less than .001).