I had a heart ablation carried out a number of years ago to deal with tachycardia issues (HR hitting 230's during episode's) caused by a tertiary pathway.

funny thing was they sent for me a "stress test" as part of the pre-op investigations which I completed without evening hitting my anaerobic threshold. i guess the idea of a "stress test" for sedentary, and usually older people isn't quite the same as what regualr ST'ers would have in mind!

I think this might be different to atrial fibrillation but the ablation has worked and I have been training away ever since, not for ironmans, but I have done plenty of sprint, oly and duathlon races