The accelerated coronary artery disease occurring in cardiac allografts is thought to be a form of chronic rejection directed against allogeneic vascular endothe-lium. If this hypothesis is correct, one would anticipate disease not only in the arteries but in venous structures as well. Accordingly, the degree of myointimal proliferation of both coronary arteries and coronary veins was assessed in 22 explanted or autopsied cardiac allografts by light microscopy. Other factors assessed included clinical cause of death/retransplantation, time posttransplantation, underlying cardiac disease, donor and recipient age, and ischemic time. Thirteen of the 22 hearts had either moderate or severe arterial myointimal thickening. Of these, 10 hearts had associated coronary venous thickening. Of the 9 remaining hearts with either mild or no arterial myointimal thickening, none had venous involvement. The overall correlation between the presence and degree of allograft coronary artery and allograft coronary vein thickening was high (r=0.80, P=0.0014). Of the other demographic factors investigated, only length of time posttransplant had a weak correlation with arterial or venous myointimal thickening (r=0.46, P=0.045 and r=0.48, P=0.039, respectively. These data demonstrate that the usually termed “accelerated transplant atherosclerosis” in the cardiac allograft is a true vasculopathy and involves both the arterial and venous systems.