Twelve single lung and nine double lung transplant recipients were studied before transplantation and at 3 months and 1 year after transplantation with serial right and left ventricular radionuclide angiograms. The resting right ventricular ejection fraction increased in the double lung recipients from 31% ± 5% before transplantation to 43% ± 11% at 3 months after transplantation (p < 0.05) and then remained stable to 1 year. The single lung recipients also demonstrated a significant rise in ejection fraction from 25% ± 11% before transplantation to 36% ± 12% at 3 months after transplantation. Again, this remained stable to 1 year. The exercise right ventricular ejection fraction also showed a significant posttransplantation rise in the double lung recipients (p < 0.005) that remained stable to 1 year. In the single lung recipients a trend was seen for a rise in the exercise right ventricular ejection fraction that did not reach statistical significance by 1 year after transplantation. Neither group had a significant change in rest or exercise left ventricular ejection fraction. The systemic blood pressure increased significantly by 1 year after transplantation in both groups. The heart rate increase with exercise at 3 months after transplantation was significantly greater in the single lung group (42 ± 13 beats/min) than in the double lung group (14 ± 13 beats/min) (p < 0.005). These data indicate that a significant improvement in right ventricular function occurs after single and double lung transplantation.