How common is a patent foramen ovale?

Common: All infants have a patent foramen ovale (pfo) as a fetus. This allows the fetal circulation to flow. Once born the pfo will close as the concentratiojn of oxygen in the blood rises. In a small percentage of infants the pfo may persist. Figures on this occurrence vary from 10-15%. Rarely is any treatment required unless the blood flow is severely affected. Most close within 1-2 years of birth.