BACKGROUND: Left ventricular hypertrophy(LVH) is known to increase the risk of sudden cardiac death, potentially in association with exercise. Increased QT disepersion(QTd) has been reported to pridict the risk of ventricular tachyarrhythmias. However, it is unknown whether various etiologies of LVH alter QTd in the same manner during and after exercise. Method: 2-D echocardiography and symptom-limited treadmill exercise test were performed in 34 hypertrophic cardiomyopathy(HCMP), 27 hypertensive hypertrophy(HTN), 20 athlete's heart(Athlete) and normal controls. QTd was measured at baseline(QTd0), at peak exercise(QTdp), after 1min (QTd1), and after 5 min(QTd5). And corrected QTd(QTcd)s were calculated. Result: Baseline QTd in HCMP group was greater than that of other groups. QTd at peak exercise of HCMP group was greater than that of other groups. There was insignificant serial change of QTd in each group. In all groups, QTcd increased at peak exercise and decreased after exercise. QTcds at baseline and at peak exercise in HCMP group were greater than those of other groups. Only in HCMP group, QTcd5 remained higher than QTcd0. CONCLUSION: Serial changes of QTcd at peak exercise and after exercise were different according to the etiology of LVH. The risk of sudden death related to exercise in patients with LVH would be different among patients with various LVH etiologies.