We present echocardiographic images of a patient with platypnea-orthodeoxia syndrome associated with the patent foramen ovale that was successfully diagnosed by transesophageal echocardiogram in the sitting position. The postural changes of the patent foramen ovale, which is difficult to detect with transthoracic echocardiography, were dynamically detected by real time three-dimensional transesophageal echocardiography. Because patients with interatrial communication are not rare, this syndrome might be overlooked in patients with unexplained dyspnea. Therefore, it is necessary to enter this entity in differential diagnosis when one sees alteration of oxygen saturation by posture change. (Echocardiography 2013;30:E116-E117).