A case of platypnea orthodeoxia syndrome: a persistent history taking was the key to the diagnosis.

A 79-year-old woman who had been suffering from dyspnea on effort for more than 50 years was admitted for further examination and treatment. On the screening respiratory examinations, the A-aDO<inf>2</inf> was elevated but none of diffusion disturbance, ventilation-perfusion ratio inequality nor right-to-left shunt was detected. Finally, the fact that the dizziness occurred only in sitting or standing position was revealed by persistent history taking. Transesophageal echocardiography in recumbent and sitting positions revealed the platypnea orthodeoxia syndrome associated with atrial septal defect. This case highlights the necessity of awareness of this syndrome and the occult atrial septal defect.