 Patients who have bypass surgery with using vein grafts from their legs saphenous veins have a very high risk of developing blockages in the grafts. It has been shown in previous studies that the progression of disease in vein grafts is very quick and can result in chest pain, heart attacks or death. In the past, evaluation of the grafts was possible with heart catheterization only. The technique of CT scan is currently considered an effective way to look at vein grafts as well as the arteries around the heart to identify blockages. 