This may help you visualize what's in there and why pains can be challenging to diagnose.patients.gi.org/topics/non-cardiac-chest-pain/
Click on the Overview and Symptoms links near the top, they
open additional sections, one showing how crowded it is in there.
You may want to consult with your family doctor, he/she can look over the E.R. results and advise you if additional tests may be advised, and I don't necessarily mean heart related, your doctor may be able to help you find the cause.
Hope this helps.