What is the best duty station to be assigned so that I can follow my cardiology treatment plan?

You're not going to get reassigned somewhere else just for heart palpitations. If the cardiologist at the MTF can't figure it out, they'll probably refer you off base.

Palpitations themselves aren't unusual or a sign of a medical issue. Sometimes I have some - usually when I'm stressed out. Sometimes I don't even think I'm stressed and they just happen. "You should contact your doctor if you experience heart palpitations frequently, for longer than a few seconds, or if they are accompanied by dizziness, loss of consciousness, chest or upper body pain, nausea, excessive or unusual sweating, and shortness of breath." That's when they are concerning if you have these other issues.

I doubt covid or the vaccine had anything to do with it. I have had the vaccine and booster - I don't have heart issues. And I had palpitations before covid existed.

If it's causing you to not be able to perform military duties, you won't get reassigned you'll probably get referred to a medboard.

Most of them have cardiologists at the local MTF and if they don't and you require ongoing care, the majority of the remaining ones will refer to to a civilian cardiologist nearby.

You need to have a discussion with your current cardiologist and determine if you need some niche specialist care that one a few locations can provide. IF so, then he help with providing documentation for you to have a compassionate request put in your file so that the appropriate level of medial services are considered when being reassigned to a new location.

However, that's a bit IF. By itself, fast palpitations are not a medically limiting (yes, they're worrying, but they aren't limiting). There are a wide variety of things that could trigger them, but it's WHAT triggers them is what would affect your assignment.