Giant Eustachian valve and Thebesian valve-A highly deceptive structures as atrial septal defect rims.

The Eustachian valve (EV) of the inferior vena cava and the Thebesian valve (TV) of the coronary sinus are incompletely regressed structures of embryonic sinus venosus. In the majority of cases, the EV and TV disappear completely after birth or are represented only by a thin crescentic fold. On echocardiography, these vestiges may mimic abnormal structures. We report a case with giant EV and TV which were initially misinterpreted as rims of an atrial septal defect (ASD) leading to the false diagnosis of ostium secundum ASD.