Ventricular tachycardia (VT) originating from the right ventricular outflow tract (RVOT) has been reported to be induced by exercise or isoproterenol and is considered to be related to catecholamines. This study was designed to examine the role of autonomic tone in spontaneous episodes of VT originating from RVOT. High frequency (HF; peak power of 0.20-0.40 Hz) and low frequency (LF; peak power of 0.05-0.15 Hz) spectral components of heart rate variability were calculated from RR intervals in a 30-min period before 33 episodes of VT during 24-h Holter monitoring in 8 patients. One VT episode was sustained, 20 were incessant and 12 were nonsustained. The ratio of LF and HF power and heart rate increased significantly from 8 min before the onset of VT, whereas the HF power gradually decreased but this decrease did not reach the statistical significance. In conclusion, an increase of the ratio of LF and HF power preceding VT suggests that activation of sympathetic tone plays an important role in the occurrence of VT originating from the RVOT.