The effect of bilateral upper dorsal sympathectomy (UDS) on cardiac function was investigated in two groups of young healthy patients who underwent bilateral excision of T2 and T3 ganglia for palmar hyperhidrosis. In ten patients echocardiography of left ventricular function (LVF) was performed before operation and 2 weeks after operation. Electrocardiograms (ECG) were done before operation, during operation immediately after sectioning each sympathetic chain, and at 2 weeks after operation. The mean pulse rate decreased significantly in patients after they underwent bilateral UDS. There were no clinical arrhythmias or changes in LVF in any patient. Submaximal exercise testing and ECG tracings done at rest and after effort were obtained for 29 patients before undergoing bilateral UDS, 30 days after operation, and 1-3 more times within a 2-year postoperative period. Pulse rates taken at rest and after effort were significantly lower than those taken after operation, and the blood pressure response to exercise was blunted. ECG tracings showed a significant change in the electrical frontal plane axis and shortening of the QTc interval. These changes were evident 30 days after operation and persisted for 2 years. In conclusion, bilateral UDS has no overt arrhythmogenic effect in the young, healthy heart and its beta-blocker-like effects persists for at least 2 years.