Two patients who underwent bypass surgery with saphenous grafts had a fistula resulting from inadvertent grafting of the cardiac vein correspondent to a targeted diagonal artery. Hemodynamic effects at rest were restricted to moderate elevation of the pulmonary blood flow, by 23 and 13% respectively, at 5 and 12 months postoperatively. No objective signs of ischemia could be elicited in either patient, in the fistula related region, and left ventricular function remained within normal limits in both cases throughout the follow-up period (36 and 24 months, respectively).