Elevation of right ventricular afterload associated with the decrease of pulmonary vascular bed is a serious problem immediately after pneumonectomy. We studied the alteration of right ventricular performance and hemodynamics by using an RVEF thermodilution catheter, and compared them among 6 patients after pneumonectomy and 8 patients after pulmonary lobectomy. Results demonstrate that 1) PVRI increased significantly immediately after the pneumonectomy, and recovered to the preoperative level on the 1st postoperative day. On the other hand, in the lobectomy patients, PVRI showed no significant change throughout the operation, because the decrease of pulmonary vascular bed after pneumonectomy was larger than that after pulmonary lobectomy. 2) In the pneumonectomy group, CI and RVEF were preserved and right ventricular works (RCWI and RSWI) increased in spite of an increase of right ventricular afterload after the ligation of the pulmonary artery. We considered that immediately after pneumonectomy the increase of right ventricular afterload associated with decreased pulmonary vascular bed was compensated by increasing right ventricular work. 3) On the 1st postoperative day, CI and RVEF did not change, but mRAP decreased significantly, and PVRI and right ventricular works recovered to the preoperative level in the pneumonectomy patients. From the above results, we considered that after the pneumonectomy, increased right ventricular afterload was compensated by the decreased circulating blood volume.