A 40-year-old woman with a significant neurological history presented with right hemiparesia, paraesthesia of the right upper member and of the hemiface. Computer tomography scanning revealed hypodensity along the right lateral ventricle which corresponded to the left hemiplegia which had developed when she was 20 years old. Arteriography of the four cervical axes was normal. Echocardiography visualized an aneurysm of the membraneous septum free of thrombosis without ventricular septal defect. The embolism was thought to be of cardiac origin and a decision was taken to correct it by surgery. Ten years after surgical repair no other neurological event has occurred.