I can't offer much since heart anxiety is my main source of anxiety, but just wanted to let you know you're not alone!
It's interesting our perception of fast. My heart rate used to be in the 80s by default, that to me was slow. It would shoot up over 100 the moment I got up and moved and easily go to 140/150 for seemingly no reason. I had this for years and it was normal to me. That's just how I was used to it. Then I had an instance where my heart went to 180 and stayed there for a few hours.
After that my GP said that didn't sound like anxiety and she put me on daily propranolol.
I've been taking that for 10 months now and my heart hasn't raced since. But now my heart rate is typically in the 60s, often even high 50s. So now when my heart goes to the 80s it feels fast and uncomfortable to me. And can really freak me out! The propranolol, as helpful a medication as it's been, has actually made me more afraid of my heart because now I feel it should no longer go faster and when it does I panic.
But the reality is, that 80 isn't fast at all!!! Normal heart rate at rest is between 60 and 100 so your heart being around 80 all day is perfectly fine! It's just heightened stress, but it's genuinely not fast. But I fully understand that it feels fast to you, because it feels fast to me now too. And I used to think it was slow. It really is all about perception!