Heterotopic heart transplantation in rats has been performed by our group since 1968. Most of our studies concerning the mechanism of immunological enhancement, the effect of immunosuppressive drugs, and the effect of pretransplant blood transfusions have been carried out using this technique. 1–5 As compared to kidney transplantation, the heart transplantation technique is relatively simple and is not hindered by the troublesome ureter anastomosing technique which is the main stumbling block for kidney grafting.