The foramen ovale is a remnant of the fetal circulation that remains patent in 20–25% of the adult population. Although long overlooked as a potential pathway that could produce pathologic conditions, the presence of a patent foramen ovale (PFO) has been associated with a higher than expected frequency in a variety of clinical syndromes including cryptogenic stroke, migraines, sleep apnea, platypnea–orthodeoxia, deep sea diving associated decompression illness, and high altitude pulmonary edema.
