Prominent Eustachian Valve Mimicking Inferior Rim of Atrial Septum Causing Iatrogenic Inferior Vena Cava Type Sinus Venosus Atrial Septal Defect

The Eustachian valve is an embryologic remnant at the junction of the inferior vena cava (IVC) and right atrium (RA). While it typically does not have any pathologic significance, veno-arterial shunting can rarely occur in patients with prominent eustachian valves and atrial septal defects (ASD), causing cyanosis and hypoxemia despite normal pulmonary pressures. We present a case of a patient with iatrogenic residual sinus venosus IVC-type ASD secondary to a prominent Eustachian valve that was misinterpreted as the inferior rim of the atrial septum during initial ASD repair.