Background: Left ventricular (LV) outflow tract (LVOT) obstruction increases mortality in patients undergoing transcatheter mitral valve implantation (TMVI) in degenerated bioprostheses, annuloplasty rings, and native mitral valves. We aimed to evaluate the left ventricular outflow tract area after TMVI using 3-diensional (3D) transesophageal echocardiography (TEE) and to investigate the pre-procedural cardiac geometry affects the LVOT area after TMVI. Methods: We retrospectively reviewed echocardiography data in 43 patients who had TMVI. A change in pressure gradient across LVOT from before to after TMVI (∆PG) and post-procedure 3D cross sectional area (CSA) at the level of the most distal portion of the mitral valve stent that was closest to the LV apex were assessed as evidence of LVOT narrowing. Results: TMVI with the use of balloon-expandable valve system was performed for 24 bioprostheses, 7 annuloplasty rings, and 12 native valves. Compared to patients without increase in LVOT gradient (∆PG <10 mmHg; n=33), patients with increase in LVOT gradient (∆PG ≥10 mmHg; n=10) had smaller LV end-systolic volume (LVESV), greater LV ejection fraction (LVEF) and smaller aorto-mitral (AM) angle. CSA at the valve stent distal edge showed strong association with ∆PG (r=-0.68, P<0.0001). Only small AM angle was associated with small CSA at the valve stent ventricular edge on multivariable analysis, independent of LVESV and LVEF. Conclusion: Pre-procedural AM angle as well as LVESV and LVEF were associated with LVOT narrowing in patients undergoing transcatheter mitral valve-in-valve, valve-in-ring, and valve-in-native valve implantation. These data may be useful for preprocedural planning.