Prolonged extracorporeal life support of pediatric and adolescent cardiac transplant patients. Options for mechanical support of pediatric patients with severe heart failure who are awaiting transplantation or have undergone transplantation are limited. This report examines 3 patients placed on extracorporeal life support (ECLS) while awaiting transplantation and 3 patients who underwent transplantation and suffered subsequent heart failure due to rejection or postoperative myocardial dysfunction. The overall survival rate was 2 of 6. The 2 surviving patients had a failing transplanted heart. There were no survivors among the patients placed on ECLS as a bridge to transplantation. In each case a contraindication to transplantation developed before a donor heart could be obtained. The mean time of ECLS support was 147.5 hours (range, 70 to 370 hours). The ECLS circuit did not affect cyclosporin levels or antirejection therapy. Extracorporeal life support can be used to support pediatric cardiac transplant patients with biventricular failure due to acute rejection or postoperative dysfunction. Although the results have been discouraging, ECLS may still have a role as a bridge to transplantation. However, complications can develop during ECLS that may preclude transplantation. 