Is it normal for my heart to beat fast when I inhale and then slow when I exhale?

I have asked other people if they have this problem and none of them do! I have heard people say the cause could be anything from a heart murmur to a medication side effect. I have had this for years and it's never sent me to the hospital or anything, but it still kind of worries me. I used to take advair for my asthma, (one of the side effects is that it kills you, no overdose or medication mix required) and I also hear it causes heart problems, which I think I believe because I haven't noticed this problem until I had gotten on that medication. I also noticed that while I was taking that medicine the my heart would tremble and feel as if it were twitching and skipping a beat, and sometimes it would feel as if it were just going to stop beating at any moment!! Can the medicine be the cause, and if not, then what could? Is it normal?