© 2017 The American Association for Thoracic Surgery Objectives: The effects of restrictive mitral annuloplasty (RMA) on subvalvular geometry remains unknown. We evaluated changes in left ventricular (LV) function, severity of mitral regurgitation (MR), and leaflet tethering parameters after RMA and clarified their associations. Methods: In 44 patients with clinically relevant functional MR who underwent RMA, distances between papillary muscle (PM) tips and anterior mitral annulus (PM tethering distance), leaflet angles relative to lines connecting annuli, and interpapillary muscle distance (IPMD) were serially quantified. Results: One month after surgery, LV function and MR severity improved with decreased anterior (34 ± 5 to 30 ± 4 mm) and posterior PM tethering distance (37 ± 4 to 32 ± 4 mm), anterior leaflet angle (32 ± 8° to 22 ± 7°), and IPMD (31 ± 6 to 25 ± 5 mm), whereas these variables remained abnormal and posterior leaflet angle increased (34 ± 8° to 48 ± 14°; P <.01 for all). During follow-up (66 ± 37 months), these effects were maintained in 33 patients without MR recurrence, whereas 11 with it showed worsened tethering with less LV function recovery. Multiple linear regression analyses identified that change in MR severity from baseline to 12-month examination independently associated with corresponding change in IPMD (parameter estimate of 0.100 with standard error of 0.039; P =.019) and that in posterior PM tethering distance (parameter estimate of −0.104 with standard error of 0.045; P =.035), whereas not with change in posterior-leaflet angle. The IPMD change was independently associated with change in LV end-systolic dimension (parameter estimate of 0.299 with standard error of 0.110; P =.013). Conclusions: The RMA procedure partially relieved leaflet tethering, evidenced by decreased tethering distances and IPMD; the latter was the main determinant of MR. These beneficial effects might be mainly attributed to post-RMA reverse LV remodeling, potentially offsetting the negative effect of augmented posterior leaflet angle in selected patients.