<s>[INST] 16 year old son, 6 ft 1, 178 lbs has had pain by left nipple, and under left shoulder blade in back for two + years, was diagnosed with costochondritis 2 years ago which has never improved, has pain daily, now feels pulsating heart in left chestnot on any meds, no previous surgeries, no other medical history [/INST] Hi thanks for contacting Chat Doctor... Here according to your complaints cardiac causes has to be ruled out. For that ECG and ECHO useful... If cardiac cause present treated accordingly... Second you had history of Costco Chat Doctor. So pain might be ongoing from that. Muscular strain can be there which lead pain... If severe pain MRI useful for sassing severity. If needed physiotherapy might help. Transcutaneous electrical nerve stimulation one of the modality for Costco </s>