Patent foramen ovale (PFO) is a hole between your heart's upper chambers. A patent foramen ovale is a small hole in the heart that may increase risk of stroke.Learn about how a PFO affect stroke risk. Patent foramen ovale (PFO) or hole in the heart, affects millions of people and can cause a stroke. PFO's don't cause strokes. Blood clots can travel from the right atrium to the left atrium and out to blood vessels of the body. Patent foramen ovale (PFO) or hole in the heart, affects millions of people and can cause a stroke. Blood thinners may be helpful for some people with a patent foramen ovale who've had a stroke. Surgery or other procedures.