Objective Decreased closing force due to left ventricular (LV) dysfunction is known to have an important role in developing ischemic mitral regurgitation (IMR). This study was conducted to explore the role of closing force in the mechanism of IMR in anterior and inferior myocardial infarction (MI). Method Fourteen patients (Anterior MI: Inferior MI=7:7, age= 60짹14yrs) with significant(> grade1) IMR underwent low dose dobutamine (peak dose: 10���/kg/min) stress echocardiography (LDSE). The apical 4 chamber, 3 chamber and 2 chamber images were acquired before and after stress. LV end diastolic volume (LVEDV), end systolic volume (LVESV) and LV ejection fraction (LVEF) were calculated by the modified Simpson���s method. The MR severity defined by effective regurgitation orifice area (ERO) was estimated by PISA method. Peak systolic trans-mitral valvular pressure gradient (trans-MV PG) was estimated by measuring peak velocity of MR jet. MV tenting area (MVTa) and height (MVTh) were measured on the apical 3 chamber view during mid systole. LV sphericity index was also calculated by the ratio of LV height to width measured on the apical 2 chamber view during mid systole. Results In the baseline characteristics, LVEDV (127짹42 vs. 85짹25ml, p=0.04), LVESV (79짹26 vs. 45짹15ml, p=0.032), EF (36짹5 vs. 45짹3%, p=0.01) MVTa (2.0짹0.5 vs. 1.2짹0.4cm2, p=0.03), and MVTh (1.1짹0.26 vs. 0.72짹0.25cm, p=0.02) showed significant differences between anterior and inferior MI groups. There was no significant difference of ERO (15짹3.6 vs. 17짹4.5mm2, p=0.54) and LV sphericity index (1.8짹0.6 vs. 2.1짹0.1, p=0.46) between two groups. In anterior MI group, all patients showed central MR jet on the apical 3 chamber view. However, in inferior MI group, only 1 patient showed central MR jet, while 6 patients represented posterior direct MR jet. LVESV (-15짹12 vs. -6짹3ml), MVTa (-0.24짹0.14 vs. -0.13짹0.23cm2), and MVTh (-0.10짹0.07 vs. -0.04짹0.06cm) decreased significantly (p<0.05) during stress in both anterior and inferior MI groups. EF (7짹5 vs. 8짹3%) and trans-MV PG (36 짹28 vs. 32짹25mmHg) also showed significant (p<0.05) increases during stress in both anterior and inferior MI groups. On the other hand, ERO increased significantly during stress in inferior MI group (8.0짹5.4mm2), while it was significantly lessened in anterior MI group (-1.2짹3.4mm2). Conclusion The result of this study suggests that the closing force plays a different role in the mechanism of IMR between anterior and inferior MI. The higher closing force gets, the less IMR develops in anterior MI. On the contrary, the higher closing force gets, the more IMR develops in inferior MI.