A case report of a triad causing platypnoea-orthodeoxia syndrome.

Platypnoea-orthodeoxia syndrome is most commonly caused by a right-to-left shunt through an anatomical defect of the interatrial septum, typically a patent foramen ovale, combined with elevated right atrium pressure. This case illustrates an uncommon cause of POS in the absence of elevated atrium pressure due to the interplay of three key elements: a patent foramen ovale, tricuspid regurgitation, and the CN. Our aim is to alert physicians to the possibility of an intracardiac shunt as the cause of unexplained and/or refractory hypoxaemia related to position changes. Early recognition of this syndrome promotes timely treatment, greatly improving patient outcomes.