After open repair of a contained rupture of a giant abdominal aortic aneurysm, the patient, a 67-year-old man, developed respiratory insufficiency, and his hemoglobin oxygen saturation dramatically decreased when his position was changed from supine to upright. Transesophageal echocardiography revealed platypnea-orthodeoxia syndrome due to a patent foramen ovale and subsequent right-to-left-shunting despite normal intracardiac pressures. After interventional patent foramen ovale closure, the patient could be separated from the respirator without difficulty.