From there, they can travel to the brain and block blood flow, causing an ischemic stroke. This does not mean that everyone who has PFO will experience a stroke or mini-stroke.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. Stroke is the major potential complication of PFO. People who have a PFO are slightly more likely to have a stroke than people who do not.