Hey snakebit, I quess you haven't been diagnosed with a heart disorder? There are several things I would consider before saying it's heart related. One is do you have a family history of Heart Disease? Are you overweight, have high blood pressure or on medications long term (other than Zoloft)?
I spent many years working in mental health so I understand your health related anxiety. Not to mention personally experiencing it myself after I became diagnosed with MS. Odd how people who are chronically ill have that anxiety issue. Now I also have extensive heart problems with an Pacemaker implant. A few months ago I started having horrible chest pain, burning, I could swear I felt my heart beating way fast, or irregular. I was freaking myself out bad even though all my tests were not showing a reason or cause for it. Then my PCP thought perhaps it was stomach related like acid reflux but extreme. I've taken multiple medications for years as well as antidepressants. He put me on Zofram and when I feel this I take one and it helps greatly.
I believe you have to consider all possible factors and hope for the best. Of course no one wants or expects to have heart problems but bottom line is....if you don't feel right then most likely something is wrong. We are always here for suggestions, support or anything at all.
I wish you much luck