Twenty-four hour ambulatory electrocardiographic recording was performed in 56 patients with variant angina admitted to the coronary care unit in order to evaluate the incidence and pathophysiology of silent episodes of ST elevation. Of 696 episodes of ST elevation of more than 0.1 mV identified during a recording period of 141 days, 531 (76%) episodes were completely silent. The incidence of silent episodes increased as the number of total ischemic episodes per day increased. Silent ST elevation revealed a significantly shorter duration and a lower intensity than symptomatic ST elevation. However, there were wide overlaps in the duration and intensity of ST elevation between silent and symptomatic episodes. In some patients, silent and symptomatic episodes of similar duration and intensity were observed. Arrhythmias during ischemic episodes such as premature ventricular contractions, ventricular tachycardia, high grade atrioventricular block, and sinus arrest were observed in 32 of 56 patients, 57% of cases and 9% of the total episodes. Arrhythmias were more common during symptomatic episodes (29%) than during silent ones (9%, p less than 0.01), but serious arrhythmias such as ventricular tachycardia, high grade atrioventricular block and sinus arrest occurred even during silent episodes. In both silent and symptomatic episodes, the duration and intensity of ST elevation were significantly lower in ischemic episodes with arrhythmias than in those without arrhythmias. These results suggest that 1) the majority of ischemic events are silent in patients with variant angina; 2) the severity of ischemia seems to be an important factor as the cause of anginal pain, but additional factors may be involved; 3) arrhythmias were more common during sympatomatic than silent episodes.