An unusual case of orthodeoxia.

Progressive hypoxia in hospitalized patients can be due to many etiologies, especially in patients with multiple comorbidities. More unusual causes of hypoxia, such as patent foramen ovale (PFO) with a right to left shunting in the absence of elevated right atrial pressures, should be considered when workup does not reveal a specific etiology. < Hypoxemia due to a right-to-left atrial shunt with normal pulmonary arterial pressures can be seen in the aortic aneurysm patients.>.