Background: The aim of the study was to compare the effects of preload reduction by nitroglycerin (NTG) on the severity of ischemic mitral regurgitation (MR) and three-dimensional (3D) geometry of mitral valve in anterior and inferior myocardial infarction (MI) with ischemic MR. Methods: Nineteen patients with ischemic MR (10 anterior and 9 inferior, 13 males, age 69 짹 11 years) were studied. Geometry of mitral apparatus including tenting volume, tenting length, and annular area and circumference was calculated with a custom quantitation software system using transthoracic 3D echocardiography at baseline and after preload reduction with sublingual NTG. LV end-diastolic and end-systolic volumes, early diastolic mitral inflow (E) and annular (E���) velocities, effective regurgitant orifice (ERO) and regurgitant volume (RV) were measured simultaneously. Results: Sublingual NTG resulted in decrease of E velocity and E/E��� suggesting reduction of preload. MR was also significantly reduced after NTG in both anterior and inferior MI by showing the decrease in ERO and RV. Reduction in MR was associated with decrease in mitral annular area (10.8짹1.9 cm2 vs. 9.2짹1.5 cm2, p=0.005) and tenting length (6.2짹2.4 mm vs. 4.5짹1.9 mm, p=0.006) and volume (6.0짹2.8 cm3 vs. 3.6짹1.4 cm3, p=0.006) in anterior MI, whereas no significant change was found in those tethering parameters in patients with inferior MI. Conclusion: Sublingual NTG resulted in reduction of MR in both anterior and inferior MI. Compared with anterior MI, patients with inferior MI showed no significant changes in tethering parameters. Thus, reduction in MR in inferior MI might not be due to changes in mitral leaflet tethering but because of increased closing forces of mitral leaflet resulted from preload reduction.