We report the first documented case of an iatrogenic aorto-coronary artery to coronary vein fistula secondary to an aortocoronary saphenous vein jump bypass graft inadvertently anastomosed to a coronary vein. Angiographic and oximetric results of left and right cardiac catheterization--including direct catheterization of the anastomosed coronary vein--as well as clinical data with a four-year follow-up are presented. The role of surgery, percutaneous transcatheter embolization, and conservative treatment is discussed in this unique case with the potential of a coronary steal phenomenon.