I agree with Mommy. This doesn't sound like it has anything to do with the heart, but everything to do with the skeleton. I wouldn't wait for it to go away, though. You should definitely talk to someone who could help. An athletic therapist would be the best. Sorry for your pain, but don't worry, it will go away!
I would talk to the athletic trainer to see what they recommend. To me it sounds more like a skeletal (ribs, sternum) problem than a heart problem....but I've never studied medicine, so I really don't know.
Good luck to you!!! I also completely understand not wanting to sit out, but you've got to listen to your body as well.