Platypnea-orthodeoxia is a syndrome characterized by dyspnea and hypoxemia on adoption of an upright posture (i.e., orthodeoxia), and by the absence or reduction of symptoms and of hypoxemia in a supine position. We describe the case of a 64-year-old patient who had developed an acute respiratory insufficiency due to right-to-left shunt in a patent foramen ovale one month after right intrapericardiac pneumonectomy. The patient was initially treated unsuccessfully with bronchodilators, corticosteroids and oxygen therapy. He was then admitted to the ICU due to severe refractory hypoxemia. Diagnosis of platypnea-orthodeoxia syndrome was demonstrated by O2 saturation and arterial blood gas analysis in the supine and upright positions. The presence of a right-to-left interatrial shunt through a patent foramen ovale was documented by transesophageal echocardiography 24 h after admission to intensive care. The next day, the patient underwent a percutaneous occlusion procedure with an Amplatzer device after consultation with surgeons and cardiologists. The patient was dismissed from the ICU after 24 hours of monitoring, and successfully discharged to home after one week.