An 80-year-old woman presented with progressive shortness of breath. There was no history of pulmonary or cardiac disease. Results of a physical examination were normal. She had significant oxygen desaturation while she was in an upright position. Admission to the hospital for workup followed, and evaluation included tilt-table transesophageal echocardiogram and cardiac catheterization. A massive right-to-left shunt through a patent foramen ovale was detected, and surgical intervention resulted in dramatic improvement of symptoms. In this patient, it seems that the syndrome of platypnea-orthodeoxia was related to aortic elongation, allowing significant right-to-left shunt.