Internal medicine
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An 84-year-old woman presented with dyspnea in the sitting position. Platypnea-orthodeoxia syndrome (POS) was suspected based on arterial desaturation when her posture changed from the supine to the sitting position. ⋯ Three-dimensional (3D) cardiac CT in the sitting position revealed that the elongated ascending aorta compressed the right ventricular inflow tract, resulting in restricted blood flow to the right ventricle and increased right-to-left shunting. This case highlights the role of 3D-CT in the sitting position in the management of POS.