If you do not have any heart issues and if it seems to be thyroid related, Its called heart palpitaions. That is, if its not beating fast all the time. Thyroid related heart palpitations come and go within minutes.
Can happen when thyroid levels T4 and / or T3 are lower than what your specific body likes. Not uncommon.
It can also happen from too much thyroid med.
So to answer your question we need to know if you have any other symptoms, hypo or hyper. And- can you post the latest T4 and T3 lab test results you might have?
my t4(ml) is 7.6 tsh .83 t3u 25.71
I forgot to mention the ranges for each test are needed to decipher the tests.
There are several ranges used in the US alone. Should be on your test sheet.