How is PFO diagnosed and treated? A patent foramen ovale is a small, flaplike opening in the wall between the upper chambers of the heart.The foramen ovale is a hole in the wall between the left and right atria of every human fetus. This hole allows blood to bypass the fetal lungs. Most people will not have any signs or symptoms directly from PFO at all. Possible PFO symptoms include: Stroke. Migraine or migrainelike symptoms Whether symptoms are due to transient ischemic attacks or paradoxical embolism is not clear. Signs and symptoms of a PFO may not occur until early or middle adulthood and may even go undetected. You passed out (lost consciousness). Bleeding is the most common risk of PFO and ASD closure.