Why are PFOs important?

In the vast majority of people, PFOs are not dangerous and are usually detected when someone undergoes an ultrasound of the heart for another reason. However, in a very small subset of people with a PFO, a blood clot that forms in your leg can cross over this flap and cause a stroke. In people in whom a stroke is thought to have occurred because of a PFO, closure of the PFO is currently recommended.