[Aneurysm of the membranous septum, left ventricular-right atrial communication and arrhythmias].

: An aneurysm of the membranous part of the interventricular septum associated with a complex congenital malformation of the endocardial cushions was diagnosed in a 39 year old woman who presented with syncope. Diagnosis was made by echocardiography and confirmed by angiography. The operative findings were: a double aneurysm of the membranous septum, a left ventricular--right atrial fistula and two hemivalves attached to papillary muscles. The usfulness of echocardiography in the diagnosis of aneurysm of the membranous interventricular septum and in the follow up of ventricular septal defects from which they arise is emphasised. The pathogenesis of the arrhythmias observed (accelerated idioventricular rhythm, reciprocating tachycardias and syncope possibly related to transient heart block) is discussed.