Abstract
Platypnea orthodeoxia syndrome (POS) can be a confounding disease. Patients with POS may have already had an extensive and unrevealing evaluation for hypoxia. POS is the worsening of hypoxia when upright compared to supine. The underlying mechanism is a right to left shunt. While there are various causes of this, we focus on intracardiac shunt. The most common of these is patent foramen ovale (PFO). Once this is identified, closure of the PFO can lead to resolution of hypoxia.