Patent Foramen Ovale

**Semantic type:** Congenital Abnormality|Disease or Syndrome

**Definition:** A persistent opening in the atrial septum after birth. While a normal part of fetal circulation, the foramen ovale should close once the newborn begins breathing and the pressure in the left atrium exceeds that of the right atrium. While a PFO is generally asymptomatic, it can lead to the passage of clots from the venous circulation into the artierial circulation, resulting in paradoxical emboli, and possible strokes.