Cor triatriatum dexter versus prominent Eustachian valve in an adult congenital heart disease patient.

An eustachian valve (EV) remnant, if present, is usually noted by the presence of a thin ridge or a crescent-shaped fold of endocardium arising from the anterior rim of the inferior vena cava orifice due to the persistence of the right sinus venosus valve. Though the embryologic explanation of cor triatriatum dexter (CTD) is the same as that of the normal formation of the EV--lack of regression of the right sinus venosus valve--it is usually called CTD or divided right atrium when there are attachments on the atrial septum giving the appearance of a divided atrium. However, it's called prominent eustachian valve when the right sinus venosus valve has partly regressed, with no remaining septal attachments and without the appearance of a divided atrium. We present the case of an adult patient with an atrial septal defect with a high insertion of a giant EV, which mimics the echocardiographic appearance of divided right atrium.