Patent foramen ovale anatomy


 * Associate Editors-In-Chief: Priyamvada Singh, M.B.B.S. [mailto:psingh@perfuse.org]; Assistant Editor-In-Chief: Kristin Feeney, B.S. [mailto:kfeeney@perfuse.org]

Overview
A patent foramen ovale or PFO is a flap-like structure in inter-atrial septum that is formed by failure of postnatal fusion of septum primum and septum secundum. It periodically opens and allows blood to shunt between the two atria. Thus, it is also sometimes called as a probe patent (PFO). This flap-like structure functions like a one-way valve mechanism that only opens to allow blood to flow from the right atrium to the left atrium during times where there is an increase flow or pressure in the right atrium. Elevation of pressure in the pulmonary circulatory system (i.e.: pulmonary hypertension, cough or valsalva maneuver) can cause the foramen ovale to open.

Embryology
During fetal development, the presence of a patent foramen ovale is necessary for life as it allows for right-to-left shunting so that oxygenated blood can flow to the left side of the heart. At the time of birth, blood begins to flow through the pulmonary circulation and this results in a rise in left atrial pressure. This rise in left atrial pressure functionally closes the flap-like structure. This functional closure is usually followed by the mechanical or anatomic closure of the structure by the age of one. A patent foramen ovale or PFO forms by failure of postnatal fusion of the two components that form the inter-atrial septum i.e. septum primum and septum secundum.