For the Quality of life (QOL) of the patients with the artificial heart system, monitoring of an information of the cardiovascular control system may be important. We’ve been evaluating an autonomic nervous system for that purpose, and recently fluctuations in hemodynamic parameters including heart rate variability (HRV) were evaluated by the use of spectral analysis and nonlinear mathematical analysis. Respiratory wave in HRV were thoght to be reflect ongoing information of the parasympathetic nerve activity. Is it true ? In order to confirm this hypothesis, we recorded vagal nerve activity directly in chronic cnimal experiments. Six healthy adult goats were anesthetized with Halothene inhalation and thoracotomy were performed by the fourth lib resection during mechanical ventilation. Arterial blood pressure, right and left atrial pressures were continuously monitored with the catheter insertion. Cardiac output were measured by the electromagnetic flowmeter attached to the ascending aorta. After the chest was closed, incision were made to the left neck and left vagal nerve were separated. Stainless steel electrodes were inserted into the vagal nerve and fixed by the plasticizer. After an incision was closed, the goats were transferred to the cage and extubated after waking. Hemodynamic parameters and vagal nerve activity were measured in the awake condition. The results showed that clear observation of the autonomic nerve discharges were embodied by this experimental system. The vagal nerve discharges were synchronized with heart beat and respiration. And tonus of the vagal nerve were significantly influenced by the hemodynamic alteration. However, respiratory wave did not always accord with tonus of the vagal nerve activity in some condition, suggesting that we must check another information to evaluate the parasympathetic tone. We must continue this study to evaluate an tunonomic nervous system during artificial heart circulation.