Lots of interesting stuff here, particularly like Tim’s response and as a few have said, there are lots of variables.
If you don’t mind, I’d like to add a bit of spin (??) maybe on this. Broadly speaking, the fitter you are, the more able your body is to cope with the demands of increased exertion. Increased muscle demands equate directly to increased blood flow and oxygenation and your cardio/aerobic fitness state will broadly define your capabilities and limitations. This means that for every “beat” of your heart, you’ll have a certain ability to satisfy those demands.
I work in a field where a HR in excess of 180/min would concern me as a clinician in the average person. The main reason for this is that over 180/min the heart becomes inefficient at pumping blood and you get cavitation in the chambers. This in turn can result in clotting and result I think we all know about. I don’t, let me say, say this to cause alarm, it’s basic physiology.
So as has been alluded to, everyone is different. At 44, I entered and completed a supersprint triathlon with barely 3 months of training. I did it on a whim, but placed well enough for me and I was without a doubt, the fittest I’d ever been in my life. Straight after the event we went on holiday and I pretty much ran everywhere with my niece and nephew, every chance I got. One day, my brother-in-law and I were having a bit of a fast walk up out of St. Ives, trying to beat the respective better halves on the bus to the car park. As we were resting, I felt dizzy and my vision blurred. I came round some 20 mins later, having collapsed and had some kind of seizure (likely hypoxia driven) and boy did I feel rough.
The upshot is really that my heart rate had not returned to normal, or near enough normal, fast enough - as a few have mentioned, this is a good indicator of your heart’s fitness.
Now I know I have a cardiac dysrhythmia. I knew about it at 40, so before the tri. But I’d trained well and carefully and survived the tri intact with no adverse affects. My own supposition, is that my HR in St. Ives stayed elevated above 180 long enough for it to be a problem, ie. increased demand failing to be met = further increased HR trying to compensate = lowering of BP = collapse (technically a vasovagal or simple faint).
I think the bottom line is, you need to pay attention to what your body is telling you - something I failed to do in the euphoria of completing the tri - and take note of your recovery to relatively normal HR and any effects that occur along the way. That should really guide your decision making processes on when to seek further professional help or not.
By all means discuss any concerns with your GP/Physician. If you have a history of heart disease in the family, they may well suggest a cardiac workup regardless of how fit you are. I’ve done an exercise stress test, pushed to 120% BRUCE protocol in order to trigger my dysrhythmia and following which I had to have an angiogram…which I got to watch on the monitor None of these things should concern you, unless you have history to worry about, family history to concern you around a certain age or there have been side effects you’ve not mentioned.