To evaluate how necessary and helpful invasive hemodynamic measurements after thoracic surgery are we studied 25 patients after pneumonectomies (n = 5), lobectomies and bilobectomies (n = 10), partial lobectomies (n = 6) and thoracotomies without lung resection (n = 4). Measurements were taken between half an hour and eighteen hours after closure of the rib cage using a preoperatively introduced Swan-Ganz-catheter. Pulmonary resistance was elevated in 12 out of 17 cases. 6 out of 25 patients had a mean pulmonary arterial pressure greater than 20 Torr. The cardiac index was below the lower limit of normal in 16 of 23 cases. 5 patients had an increased stroke work index. There was no correlation between the hemodynamic parameters and the type of surgery. In 7 patients the measurements indicated hypovolemia. Isolated right or left sided cardiac insufficiency was noted in one case each. Four patients received nitroglycerin intravenously resulting in a dose-dependent reduction in pulmonary arterial pressure, pulmonary resistance and heart work. Hemodynamic monitoring with a Swan-Ganz-catheter seems not to be necessary in every case. But it proved to be a safe method which can help in the management of high-risk patients.