RÉSUMÉ
A 63-year-old-man with significant left hemiplegia was admitted to hospital. He had experienced a transient cerebral ischemic attack 10 years ago. Computed tomography revealed hypodensity along the right lateral ventricle, which corresponded to the left paralysis. Echocardiography and left ventricular angiography revealed an aneurysm of the membranous septum (AMS) without a ventricular septal defect (VSD). Therefore, the embolism was thought to be of cardiac origin, but surgery revealed that it was not caused by AMS. The aneurysm was created when the septal leaflet of tricupid valve formed a giant capsule during the process of natural closure of the VSD. It was a large pouch, 2.0 cm in diameter, adjacent to the septal leaflet. Anomalies of the tricuspid valve, including pouches, can resemble AMS.
