Thanks, Peter. I'm already on bog standard T2 diab/cardiovascular meds, i.e. metformin, clopidogrel (platelet population limiter) & pravastatin, none of which [should] have a direct effect on rhythm. Mostly I notice my heart wambling (technical term) after a ride where I've pushed harder than I ought to, and what I get then falls into two categories: (1) regular atrial+ventricular beat pairs at around 1/sec with the odd "missed" beat or (2) regular ventricular beats with the odd "fizzing" sensation where the atrial beat ought to be. However, I've been noticing this for ~20 years with no obvious TIAs or ill-effects.
I suspect (2) to be AF, and while I'm looking for corroboration I'm also wondering if there's anything harmless that could cause it. I'm due to see my cardiologist in late September. He's a great fan of beta blockers when there's a whiff of anything untoward, however trivial. I am not.