Not sure about irregular heart beats. But when I was burning out from my PhD a very heavy and intense heart beat was the most notable physical symptom. There was no underlying problem, I was just going through a great deal of emotional stress.

The problem with anxiety is that it leads to intense heart beating and your anxiety then leads you to assume something physically wrong with your heart. You don’t think rationally on stress!

Yes https://www.nhs.uk/conditions/heart-palpitations/

Does myocarditis produce ectopic heartbeats?