I tend to think it is more of a muscle thing with me than heartburn. My first 'symptom' of this damn mirena was actually a horrible pain that went from my chest all the way to my back. The pain would sometimes be right beneath my chest and other times down closer to my heart, but it was so intense I thought I was having a heart attack or something. I went to the ER and they did EKG's and Xrays and saw nothing. I think for me it is a muscle thing, like my legs feeling horribly weak and in pain, and my neck being tight, etc. Maybe it is heartburn, idk... but when I get heartburn I tend to have reflux and a feel it boiling and the chest pain i get is different from that...