Patients with ischemic heart disease have many episodes of ischemic attack which is presented as ST-T change in electrocardiogram during ordinary daily life. The purpose of this study was to confirm the presence of a significant circardian variation in transient myocardial ischemia and the difference of the incidence of ischemia according to involved vessel.

Twenty two patients with angiographically significant coronary stenosis were evaluated. The ambulatory electrocardiography(Holter monitoring) was performed in each patients.

One hundred twenty-eight episodes of ischemic ST-T changes occured in 18(82%) of 22 patients and 65(51%) episodes of ischemic ST-T changes occured between 6 A.M. and 12 noon(p<0.005). The mean frequency per patient according to involved vessel was 9 in double vessel disease, 4.5 in diffuse sclerosis with old myocardial infarction, 2.9 in single left anterior descending, 2.3 in single right coronary and 1 in single left main coronary artery disease. The only one episode of T wave change was observed in patients with lesion of left circumflex artery. The mean frequency of ST changes per patient according to type of angina was 4.8 in postinfartion angina, 3.5 in unstable angina and 2.1 in stable angina and the mean frequency of T change was 4.7 in stable angina, 2 in unstable angina and 0.3 in postinfarction angina.

The significant circardian variation of ischemic activity was found in patients with ischemic heart disease. The mean frequency of ST change was higher in double vessel disease and diffuse sclerosis with old myocardial infarction than in other coronary artery lesion. And the episode of ST change was more frequent in postinfarction angina and unstable angina pectoris and the episodes of T change in stable angina pectoris. Also this study suggest 24-hour Holter monitoring has a low detectability of ischemic episodes in patient with lesion of left circumflex artery.