The foramen ovale is a small hole or channel in the wall between the top two heart chambers that allows oxygenated blood to mix in a baby before it is born. After a baby is born, the foramen ovale typically closes although for perhaps 20-30% of us, a channel persists and is termed a patent foramen ovale (PFO). In unusual situations, a clot from the veins of the body can pass across this channel and find its way into the brain circulation.