Aneurysm of the interventricular septum without a shunt was found by means of transthoracic echocardiography in a 6-year-old boy with acute hemiparesis. Until the time of the incident, he had been healthy. The aneurysmal sac contained 2 clots, presumably resulting in the ischemic cerebral infarct. On the basis of the echocardiographic scan, successful surgery was performed. To the best of our knowledge, this is the first report describing such dramatic sequelae of interventricular septal aneurysm.