"Heart attack" is a bit misleading - it's usually not your run-of-the-mill coronary occlusion but rather cardiac arrest. A couple of articles (the second one uses far too many quotation marks but otherwise ain't bad):
https://www.theguardian.com/lifeandstyle/shortcuts/2012/mar/19/cardiac-arrest-heart-attack-differencehttps://fitnessnothealth.wordpress.com/category/footballers-and-heart-attacks-heres-why/From what I can gather the type of cardiac arrest footballers etc. are prone to is very hard to predict even when the causes are known.
Anecdotal corroboration on state of medical knowledge & reliability of observation of cardiac performance:
Our club prez, DZ, had a cardiac wamble (tech. term) in Belgium a couple of years ago, fell off his bike and was taken to hospital where life-threatening arrhythmia was diagnosed. After a few days under observation he was packed off home with orders to see his own cardiologist PDQ, which he did. A stress test showed arrhythmia setting in at ~130 bpm, so he was told to take it easy.
He had another wamble a week later, and after tests was told to keep it under 100 bpm, which he normally attains going upstairs. A follow-up showed arrhythmia at 86 bpm.
He then asked the cardio if arrhythmia and possible arrest were as likely at 80 bpm as 150, cardio said well, yes, probably. DZ said "I might as well ride my bike then". Well, yes.
He's been riding since. Sunday we're doing a 130k with 1450 metres of climbing.
