Loose rivets, I too was aware of the theory regarding the small hole in the heart and I had read that this possibly was linked to increase risk of minor strokes. This seems to have a greater impact on divers according to limited research and may lead to greater chances of developing a bend while on deeper dives.
I dive regularly and due to this I thought I would mention it to my doctor recently, as well as the fact that although I have not had one of these migraines for several years now I want to know if the stroke risk is there(At this time I was not aware it could affect my class 1). I also showed him some supporting research, I expected him to tell me not to worry but instead he referred me to a specialist in order to give me peace of mind. This involved a discussion with the specialist, then an ultrasound scan of my heart. I havent had the formal results (I have another appointment soon) but the person doing the scan said they could find no sign of a hole. This however may not mean anything as in my case it only becomes apparent during extreme excertion and therefore it may require a large increase in blood pressure to start the process.
Alternatively it may now have healed explaining why I have not had a reoccurrance for some time.
I now need to ask the specialist to write a report for the caa in order for them to consider my fitness for a class 1.
For your info these are the articles I presented to my doc, who was not familiar with the research at that time.
http://www.sciencenews.org/articles/20050219/bob8.asp
http://www.clinsci.org/cs/100/0215/1000215.pdf