Prominent Eustachian valves, with obligate right-to-left shunts, have been reported as a cause of neonatal hypoxemia. This anomaly can present as an obstructive structure that inhibits antegrade flow through the tricuspid valve and furthermore contributes to right-to-left atrial shunting in the presence of a patent foramen ovale or atrial septal defect. This case highlights the evaluation and diagnostic workup for chronic hypoxemia in an adolescent female patient and considerations for percutaneous atrial septal defect closure.