A 90-year-old patient with emphysema-fibrosis syndrome was hospitalized for dyspnoea. On admission, she was in respiratory distress, with cyanosis, jugular veins distention, and lower limb oedema. Chest X-ray (CXR) showed a right pleural effusion. Just after pleural drainage, she developed cyanosis and altered consciousness. SpO2 dropped from 91 % to 74 %. Point-of-care lung ultrasonography and CXR excluded a pneumothorax or re-expansion pulmonary oedema. Echocardiography revealed right heart dilation, pulmonary hypertension, and a patent foramen ovale (PFO) with a large right-to-left shunt. Platypnoea-orthodeoxia syndrome (worsening oxygenation when standing improving in supine position) was diagnosed. This rare condition caused by right-to-left shunts should be detected because correction may improve patient outcomes.