Heart rejection is a major problem for heart transplant patients. The best strategy for understanding and preventing organ rejection is to study experimental animal models. The popular mouse model of heterotopic cardiac transplantation has been used for over three decades to help investigators understand the pathogenesis of graft rejection and in turn, how novel drugs can attenuate the immune response to transplanted organs. Also, since the genetic blueprint of mice is well-known, specific genes can be modified to study its effect on graft acceptance and tolerance. Despite the large potential...