This article describes the development of a new experimental model using rats for the evaluation of small-caliber vascular grafts. By modifying heterotopic heart transplantation, two 1.5- to 2.0-cm long vascular prostheses were interposed between a syngeneic donor heart and the recipient abdominal vessels in the form of vascular bridges. Once blood flow through the vascular grafts was reestablished, the donor heart resumed normal beating. The status of the vascular grafts could be easily monitored by palpation. Occlusion of the grafts stopped donor heart beating without affecting survival of the animals. Once the surgical method was mastered, the postoperative mortality was approximately 10%, and the total procedure took less than 2 hours. Although microvascular surgical technique and equipment are required, this model has several advantages, including easy detection of thrombotic occlusion of the grafts, the use of small animals of defined genetic background, the absence of effect of graft occlusion on the recipient's life, and possible repeated operation on the same animal.