In order to evaluate whether variations in autonomic nervous tone have a significant role in the induction of coronary arterial spasm in variant angina, we analyzed the changes in heart rate variability (HRV) related to spontaneous episodes of ST-segment elevation, recorded during 24-hour ambulatory ECG monitoring, in 13 patients with variant angina (9 men and 4 women, aged 63 +/- 12 years). In order to obtain an accurate analysis of HRV changes, we only included ischemic episodes characterized by silent ST-segment elevation, lasting at least 3 min and without any ST change in the previous 30 min. HRV indexes in the time domain (RR interval, standard deviation of RR intervals [SD], pNN50, r-MSSD) and in the frequency domain (LF = 0.04-0.15 Hz, HF = 0.15-0.40 HZ, LF/HF ratio) were calculated on 2 min intervals, centered at 15 min before (15B), 5 min before ed 1 min before (1B) the appearance of ST elevation, as well as at peak of ST-segment elevation. Of 161 ischemic episodes found on 24-hour Holter recordings, 60 (37%) fulfilled the inclusion criteria for analysis (4.6 +/- 3.5 episodes/patient, range 1-12). The duration of the selected episodes was 6 +/- 2.5 min and ST elevation was 2.2 +/- 1.0 mm. Heart rate (HR) did not have any change before ST elevation, whereas it showed a small, but significant increase at peak ST (73 +/- 12 versus 67 +/- 11 b/min at 15B, p < 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)