An 80-year-old female presented with progressive breathlessness, worse on sitting or standing and relieved by lying flat. Subsequent investigations identified a patent foramen ovale (PFO) with right-to-left flow across the interatrial septum (IAS). A diagnosis of platypnoea orthodeoxia syndrome secondary to inter-atrial shunting was made. Technical features precluded a percutaneous PFO closure so an open surgical repair was performed with complete resolution of symptoms. We discuss the pathophysiology and management of platypnoea orthodeoxia syndrome.