Although the autonomic nervous system has been implicated in the genesis of coronary spasm, the precise mechanism by which it serves as the trigger of coronary spasm remains unclear. The aim of this study was to investigate changes in autonomic nervous activity associated with ischemic episodes in patients with variant angina (VA). Heart rate variability (HRV) on Holter monitoring was analyzed during 17 ischemic episodes in 11 patients with VA. The parameters of HRV were measured during a 2-min period at various time intervals prior to the onset of ST-segment elevation. The low frequency (LF) and high frequency (HF) components of the HRV, LF/HF ratio, mean RR interval, and the coefficient of the RR interval variation (CV) were calculated for each time interval. Both the HF and the CV increased significantly in the 2 min prior to the onset of ST-segment elevation, suggesting heightened vagal activity. The LF/HF ratio, a measure of cardiac sympatho-vagal balance, did not change. The LF, a measure of sympathetic activity with vagal modulation, also did not change. The RR interval decreased significantly in the 2 min prior to the onset of ST-segment elevation. These results suggest that enhancement of both the vagal and the sympathetic nervous activity plays an important role in the initiation of coronary spasm.