BACKGROUND: In general, we know that a thoracic sympathicotomy may have influence an cardiac autonomic nervous activity to change vital signs. The purpose of this study was to analyse preoperative and postoperative heart rate variability to evaluate the influence of a sympathicotomy on cardiac autonomic activity. METHODS: We studied 14 healthy patients, ASA physical status I and II, undergoing an endoscopic thoracic sympathicotomy. A laryngeal airway mask was performed on all patients for tracheal intubation. Intravenous anesthesia was induced by administration of propofol 10 mg/kg, and fentanyl 2ng/kg and was maintained with propofol 10ng/kg/hr and N2O-O2 (2 L/min-2 L/min). An electrocardiogram was checked in the supine position with Biopac Student Lab. at an hour before anesthetic induction, after a left and right sympathicotomy and at 3 - 4 hours after emergence. A spike 2 version 3.0 was used for analyzing heart rate variability and a Fast Fourier Transform was used to yield a power spectrum. Frequency bands were divided to low frequency (0.02 - 0.09 Hz), middle frequency (0.1 - 0.15 Hz), and high frequency (0.16 - 1.0 Hz) components. RESULTS: There were no significant changes of heart rate, high frequency component, low frequency component and ratio of low to high frequency component. CONCLUSIONS: Influence of a thoracic sympathicotomy on cardiac autonomic activity was less in the supine position at rest. However, we think that the response of the cardiac autonomic activity to sympathetic stimulation like position change and exercise after a sympathicotomy may yield different results and studies about this must be done.