Development of a soft, pliable, slow heparin release venous graft. To prevent their collapse, a certain amount of stiffness is generally required for prosthetic venous grafts, so EPTFE grafts have been used. However, the native vein is pliable without any stiffness. We developed a soft and pliable graft that can maintain patency of the lumen because of its compliance. Fresh porcine ureter was incubated in a ficin solution to remove cell components and noncollagenous proteins. One percent protamine sulfate solution was injected into the ureter lumen to impregnate the inner surface. The ureter was then crosslinked with a 1% glutaraldehyde solution, dipped into a 1% heparin solution for 5 hours, and rinsed with distilled water. This procedure made the ureter very soft and pliable, and also conferred antithrombogenicity to the graft by heparinization. The grafts were implanted into the posterior vena cavae of 20 dogs and were removed from 1 to 878 days after implantation. Eighteen grafts were patent, but two grafts were occluded at the anastomotic site at 218 and 107 days, respectively. As a control experiment, nonheparinized grafts were implanted into 15 dogs; all were occluded with fresh thrombi. All the patent grafts kept their original elasticity, which allowed them to heave in unison with the heartbeat, and were similar in appearance to the native vena cava. Heparinization was effective in preventing thrombus formation. These results indicate that this type of graft is an ideal prosthesis as a venous graft, having physiologic properties such as compliance and antithrombogenicity. 