Thanks SurgiMenopause a closer reading does suggest another interpretation.
I believe rohilla is describing the pain, not saying his son was biting his nails. Rohilla- here's a copy of what I replied to your other post:
You may want to ask the doctor to do a nuclear medicine test to see how the heart functions under stress and and in a resting state, to see if there are areas of the heart that are not receiving the kind of oxygen it should. Did they do any cardiac enzyme blood testing to look for elevations?
But since you mention bronchitis in this post, something that can be very irritating to the chest wall, you may want to ask your doctor about costochondritis as well, which can be very painful and even cause pain to take a deep breath with it. Also, esophageal spasms can feel very much like a heart problem, so if it turns out it's not the heart or costochondritis (and the lungs look okay with an x-ray), you might want to pursue getting him referred to a GI specialist to see if he is having an esophageal issue.
Thanks for sharing and you should consult with a doctor. It could be related to prior pulmonary issue...possibly a heart problem. There could be an anxiety problem with the nail biting.