Left ventricular outflow tract obstruction (LVOTO) is a critical complication after mitral bioprosthesis. Intraoperative transesophageal echocardiographic (TEE) monitoring enables early diagnosis and guides prompt subsequent treatment. Here we report a case of mitral heart disease who developed critical LVOTO following mitral xenograft replacement. The values of intraoperative TEE in the disclosure of the LVOTO and its facilitation of successful management are discussed.