Tricuspid pouch forms during the spontaneous closure of a ventricular septal defect (VSD). Cases have been reported in which the tricuspid pouch was discovered for the first time during surgery and could not be distinguished from an aneurysm of the membranous septum( AMS). A 58-year-old woman had a heart murmur. Transthoracic echocardiography showed an aneurysm-like pouch protruding into the right ventricle. Magnetic resonance imaging could not distinguish between AMS and tricuspid pouch;however, contrast-enhanced computed tomography showed a VSD. The membranous structure comprised multiple lobules, and the tendon of the papillary muscles was continuous with the tricuspid valve. Intraoperatively, the tricuspid valve septal leaflet was adhered to the defect hole. It was incised along the annulus, the VSD was closed with a bovine pericardial patch, and the annulus of the tricuspid valve septal leaflet was suture closed. The patient was discharged after a good postoperative course.