The paradox of platypnoea–orthodeoxia syndrome

Platypnoea–orthodeoxia is a rare clinical syndrome characterised by dyspnoea and oxygen desaturation in the upright position which improves when supine. It requires two components: a sufficiently sized anatomical vascular defect (typically intra‐cardiac or intra‐pulmonary) combined with a functional component that promotes positional right‐to‐left shunting. We describe the rare occurrence of a patient with platypnoea–orthodeoxia syndrome (POS) because of a paradoxical shunt through a patent foramen ovale caused by a large right atrial line‐associated thrombus in a male with metastatic oesophageal cancer undergoing chemotherapy. This case is a timely reminder to consider POS amongst differentials for hypoxia as it is often treatable if recognised.