@KoiwiGal - I think it all depends on how big the hole is. Since it allows some blood to bypass the lungs, it can make breathing very difficult, especially for a baby who won't have very developed lungs anyway.
But, if it is just a small hole, I don't think it would make all that much difference to blood flow.
I didn't know about the link between PFO and migraines though, or even the link between PFO and strokes.
I guess I thought the surgery was always to make it easier for blood to get to the lungs.