Medical Animations: Patent Foramen Ovale

The foramen ovale is a natural opening that exists between the right and left atria in the fetal circulatory system. A patent foramen ovale, or PFO, is a type of atrial septal defect. The hole usually closes after the infant takes its first breath. If it fails to close, it is considered patent, or open. A PFO does not always cause health problems.