SUMMARY Twenty-four-hour ambulatory ECG recording was performed in 26 patients with variant angina to evaluate the diurnal distribution of ST-segment elevation in relation to chest pain and the incidence of arrhythmias during the episodes. During a recording period of 52 days, 364 ST-segment elevations of 1 mm or greater were observed and 79% were asymptomatic. ST-segment elevation frequently occurred between 0:00 and 9:00 hours (72%) and most frequently between 5:00 and 6:00 hours (13%). Only a few episodes occurred between 10:00 and 18:00 hours. Premature atrial contractions, premature ventricular contractions (PVCs), ventricular tachycardia (VT) and complete atrioventricular block occurred during 12% of the episodes and were more common during painful episodes (32%) than during painless ones (6%). However, VT and severe forms of PVCs (couplets and bigeminy) appeared eight times during painless episodes and nine times during painful ones. Arrhythmias occurred more frequently when the elevated ST segment started to return or was returning to the control level (n = 38) than when the ST segment was rising (n = 8). The incidence of arrhythmias was lower when the daily frequency of ischemic episodes was high. This study shows that episodes of asymptomatic coronary artery spasm predominantly occur early in the morning as symptomatic episodes; complex dysrhythmias appear during the asymptomatic episodes; arrhythmias occur predominantly during a "reperfusion period;" and more arrhythmias accompany infrequent daily episodes of ischemia than frequent ones.IN PATIENTS with variant angina, anginal attacks occur more frequently at midnight or early in the morning, and arrhythmias, including life-threatening ones, are common during the attack. 1-3 To our knowledge, however, no quantitative data have been reported on the diurnal distribution of ischemic episodes, such as chest pain and ECG changes, in variant angina except for a preliminary report by Kuroiwa,4 which showed a higher frequency of recurrent ST-segment elevations early in the morning. It is important to clarify the diurnal distribution of the episodes for the evaluation of pathophysiology of variant angina as well as for treatment.ST-segment elevation without pain has been observed in variant angina and recently proved to be due to coronary vascular spasm resulting, like painful STsegment elevations, in myocardial ischemia.5-7 Twenty-four-hour ambulatory ECG monitoring is a good tool for evaluating ST-segment elevation in variant angina, especially that without chest pain,2' 8.9 and can also be used to evaluate arrhythmias during the episodes.In the present study, we studied the diurnal distribution of ischemic episodes with or without chest pain and the incidence of arrhythmias during the episodes using 24-hour ambulatory ECG recordings. Materials and Methods Twenty-six consecutive patients with variant angina admitted to our clinic from June 1976 to December 1981 were studied. Twenty-five were males and one was female, ages 44-72 years old. None of these patie...