Platypnoea-orthodeoxia (PO) is a condition with dyspnoea and arterial deoxygenation during orthostasis, which is relieved in the supine position. This is a review of the background of PO, which is always an orthostasis-related right-to-left shunt of deoxygenated blood either across a persistent foramen ovale/atrial septal defect or an anatomical or functional pulmonary shunt, and diagnosis and management is discussed. PO is considered to be rare but will presumably be diagnosed increasingly frequently with increased use of pulse oximetry and functional imaging including echocardiography with bubble-contrast.