Is the concern that he will be/is placed on blood thinners (Warfarin, Plavix, Xarelto, etc.) and that will cause the problem? I'm not aware that AFIB of itself causes bleeding but usually they put you on thinners if you have it because it tends to cause blood clots. If 'thinners' is the question, then yes I ride while on blood thinners and several other folks on here do also. I recently had an arterial blood clot in my left leg removed (apparent result of an aneurysm surgery) and they checked for all sorts of stuff (but AFIB did not show up for me). I'm on thinners now (Xarelto) as a result of the removal surgery and damage to the artery. I don't think anything about it (recently did 6,700+ mile ride across the USA) because if I crash, I figure there will be other issues to deal with. ;-) Thinners don't mean you don't clot, it just takes a lot longer. And with some like Warfarin, they have 'instant' fixes like a megadose of vitamin K. I would definitely include the information in his ICE information. Hope that gives your friend some helpful information.