When your immune system activity increases, generally so does your heart rate. It's fairly common to get sick and have an increased heart rate. A quick search for "heart rate when sick" will turn up a number of results explaining this, the mechanisms behind it, and more.

Sorry you missed out on simple, effective preventative health measures because of this misunderstanding.

I got two. But these events started to happen 4 years after my last shot.

An immune response to any trigger temporarily increases the heart rate.

Or Covid itself.

COVID vaccines (and various other vaccines), often cause flu-like symptoms for a day or so; you should've been warned about this at the time. Pretty much anything that gives you a fever will boost your heart rate a bit.