The potential risk of the open foramen ovale is in the possible penetration of thrombi from the venous system to the left atrium and subsequently to the left systemic circulation. In patients with TIA or CMP in their history and with a proved right-left shunt by the open foramen ovale, four treatments are recommended: a surgical closure of the foramen, cathetrisation closure, antiaggregation therapy and anticolagulation therapy.