Heart rate variability (HRV) is increasingly recognized as a means of evaluating cardiac autonomic tone. Our group previously has demonstrated that thoracic epidural anesthesia (TEA) successfully suppressed the electrical storms in patients. However the effect of TEA on HRV during sympathoexcitation remains unknown. Our objective of this study was to determine the effects of stellate ganglion (SG) stimulation on HRV by using power spectral analysis as well as the effects of TEA on HRV response to SG stimulation. After insertion of an epidural catheter from T7/8 placing distal tip of the catheter to T1 level, a median sternotomy was performed to expose the heart and the bilateral SG. A 56‐electrode sock was used for obtaining epicardial activation recovery interval (ARI), a surrogate marker of action potential duration. Fifteen anesthetized pigs received SG stimulation at 5 Hz for 30 second. SG stimulation significantly increased low frequency normalized units (LF n.u.) component (42.7±9 vs. 12.4±3 baseline, p<0.05) indicating enhanced sympathetic nerve activity and decreased high frequency normalized units (HF n.u.) component (26.5±3.2 vs. 56.4±10 baseline, P<0.05) indicating a decreased parasympathetic nerve activity. As a result, LF/HF significantly increased from 0.22 to 1.61 during SG stimulation. LF component significantly correlates with ARI (r=0.81) and ARI dispersions (r=0.85). TEA significantly attenuated the LF/HF from 1.6 to 0.6 with increased HF components from 26.5±3.5 to 48.2±4.1(n.u.). In conclusion, HRV can precisely reflect the cardiac autonomic tone and TEA modulates the HRV by enhancing the HF components. LF (n.u.) HF (n.u.) LF/HF Baseline 12.4±3.2 56.4±10.1 0.22±0.1 SG stim 42.7±8.5 26.5±3.2 1.6±1.0 SG stim + TEA 37.7±6.2 48.2±4.5 0.78±0.1