Indications for the use of direct mammary artery and vein graft are emerging from critical review of results in over 2,000 patients following myocardial revascularization. Factors such as patency, stenosis, late changes, adequacy of flow, choice of recipient vessel, and myocardium play a role in determining whether mammary artery or vein graft will be of optimal value. Average flows in veins are substantially greater than in the mammary artery. In our cases the right mammary artery had the least flow. Patency with mammary artery was higher than veins, but when flow was greater than 70 ml/min in veins, long-term patency was 90%. When vein flow was low, late closure was increased and mammary artery offers superior results. Potential for high or low flow was a critical differential point in choosing the bypass vessel and was determined by utilizing angiography, ventriculography, and intraoperative evaluation.