Left ventricular outflow tract (LVOT) obstruction is a feared complication of transcatheter mitral valve replacement (TMVR). This procedure leads to an elongation of LVOT in the left ventricle (namely, the neoLVOT), ultimately portending hemodynamic impairment and death. This study sought to understand the biomechanical implications of LVOT obstruction in two patients who underwent TMVR as an "off-label" application of the Edwards SAPIEN 3 (S3) Ultra transcatheter heart valve (THV). A computational framework of TMVR was developed to assess the neoLVOT area and quantify the sub-aortic flow structure. We observed that the annuloplasty ring serves as the key anchor zone of S3 Ultra THV. A good agreement was found between the numerically-predicted and CT-imaging measurements of neoLVOT area, with differences less than 10% in both patients. The pressure drop across the neoLVOT did not determine hemodynamic impairment in both patients. Quantification of structural and hemodynamic variables by computational modeling may facilitate more accurate predictions of the LVOT obstruction in TMVR, particularly for patients which are considered to have a borderline risk of obstruction.