I know what you mean about the heart thing. When I get a panic attack sometimes my heart races, but other times it "thumps" or "pounds". It's not an especially fast heartbeat, but rather a dull, but more intense and more powerful one. It feels like my heart is on the verge of either breaking through my chest or literally exploding. I've even felt sore the next day (like I pulled a muscle). It was really scary at first, but I've come to understand that it's part of how my body responds to anxiety. I still don't like it, but I accept it. By not fighting, I find that it doesn't last as long.
If you can't find anyone to talk to, can I suggest you start writing your thoughts and feelings down? I feel guilty "bothering" people with my problems and have always been the listener, not the talker. So in addition to therapy I started journaling when I feel my anxiety come up. Even if I don't know what I "need to get out", I will just start writing. It has really helped in my case. It may not replace another person who can offer back support and/or ideas, but it's a useful tool nonetheless.
It's like we have these toxic thoughts and worries that have to come out one way or another. You can talk to another person, you can talk out loud to yourself if that helps, you can write them down, you can type them on a computer, etc. or you can push them down and wait for it to come out physically, such as in a panic attack.