Patients who have had a stroke or TIA and have a PFO have about a 1-3% per year chance of having another stroke.
Certain factors may make the risk of subsequent strokes even higher. If the tissue of the PFO is very mobile, it is called an atrial septal aneurysm*. In patients with atrial septal aneurysm, the risk of recurrent stroke may be as high as 5% per year.
* Atrial septal aneurysm should not be confused with blood vessel or brain aneurysms that are an unrelated problem