The sensitivity and specificity of ST segment change on ECG for detection of coronary artery disease(CAD) by pacing stress test were assessed. Among 28 cases with chest pain(mean age 52, M/F : 21/7), 10 patients had normal coronary angiographic finding(Group I), and 18 had coronary artery disease(Group II). Pacing stress test showed high specificity(100%), but low sensitivity(61%) for the diagnosis of CAD. Especially in patients with 1 vessel disease, the sensitivity was only 50%, and positive results were not attained unless there was at least 90% or more stenosis in any of the major branches(LAD, RCA or LCX). But in patients with multivessel disease, the sensitivity was much higher(83%). Lateral(V4-6) or inferior leads(2, 3, aVF) showed ischemic ST segment depression most commonly. Therefore one of the inferior lead and V5 may be a minimum requirement for monitoring pacing-induced ST segment changes. Time constant during isovolumic relaxation showed statistically significant prolongation after pacing only in CAD patient group, suggesting pacing-induced impairment of early left ventricular relaxation.