Is it a secondary effect from a long-ago incident? Is this common in aging endurance athletes? I remember when Tony came down with atrial fibrillation, he researched and found high incidence in (former) long distance runners. As far as I know he controls it with medicine.
MR (mitral valve regurgitation) is, in my case, pretty much a consequence of high blood pressure over years (even tho treated in recent years). The left ventricle pumps against an increased afterload (systemic vascular resistance) over time and can become thicker and less compliant. The mitral valve may prolapse as a response and allow blood to back flow into the left atrium. All the valves and all the kings' men for a pump to work efficiently.
Atrial fibrillation can be the consequence of several things, most age-related. AF is probably down the road for me. I have a large left atrium as a consequence of the MR which can lead to AF. Obviously, I'll get some expertise if not a new heart (just joking). There is mitral valve repair if/when indicated. Atrial fib can be controlled by meds or ablated by radiofrequency depending on situation.