RESUMEN
BACKGROUND: Platypnea-orthodeoxia syndrome is a rare condition characterized by onset or worsening of dyspnoea with orthostatism (platypnea) and arterial desaturation (orthodeoxy) that is relieved by returning to a recumbent position. An acute event causing a change in the pressure relationships inside the cardiac chambers can lead to the diagnosis of a previously undiagnosed cardiac anomaly, as the following case illustrates. CASE SUMMARY: A previously asymptomatic 80-year-old female patient was admitted in our hospital with a sudden onset ischaemic stroke. Initial evaluation, including 12-lead electrocardiogram and transthoracic echocardiogram, was unremarkable. During hospital stay, she develops pulmonary embolism, after which she complains of positional dyspnoea that develops upon sitting up, accompanied with refractory hypoxaemia that reverts on recumbent position. Transoesophageal echocardiogram revealed an interatrial septum with an exuberant hyperdynamic movement, and an abundant passage of contrast from the right atrium to the left, even without performing the Valsalva manoeuvre, compatible with an important patent foramen ovale. A percutaneous closure was performed, and patient has been symptom-free since then. DISCUSSION: This is a case illustrates how an anomaly that has been present for 80 years can suddenly manifest itself with an array of different symptoms that can make the diagnosis challenging. A high degree of clinical suspicion is crucial for an accurate diagnosis and definitive treatment.