Background: The aim of the study is to investigate the determinants of the exercise-induced dynamic LVOTO and its clinical significances. Methods: In 763 patients who underwent symptom-limited exercise stress echocardiography (ESE) for exertional chest pain or dyspnea, 177 patients were excluded Dynamic LVOTO was defined as the peak pressure gradient at LVOT > 40 mmHg immediately after exercise by Doppler study. There were 139 patients (M:F=104:35) with dynamic LVOTO (group A), and 447 patients (M:F=248:199) without dynamic LVOTO (group B). Results: In group A, the incidence of hypertension, male sex, diabetes, and negative ESE test were more frequent compared with group B. Echocardiographic parameters including end systolic left ventricular dimension and LVOT index (LVOT dimension/body surface area) were smaller in group A. Resting and post exercise septal annular systolic velocity (S���), and left ventricular ejection fraction were higher in group A. In multivariable analysis, negative ESE test and LVOT index showed significant correlation with exercise-induced dynamic LVOTO (p=0.001, and p=0.048, respectively). Among the patients with negative ESE test, positive treadmill test was noted in 14.9% (75/505) of the patients. The frequency of dynamic LVOTO with positive treadmill test (41.3% [31/75]) was higher than with negative treadmill test (23.5% [101/430], p<0.005). Conclusion: Vigorous left ventricular contraction and small LVOT index caused exercise-induced dynamic LVOT obstruction, which might be related to false positive exercise ECG test.