i also have gotten a pain in my heart area, left center side of the chest, and am pretty sure that jwh-018 is at the very best making the pain worse. smoked it for months without any bad side effects. then i started to notice a mild pain, which eventually got stronger, and appeared periodically when i was not high, and even several days after getting high, it seems to be pretty much permanent now, although i smoke very little jwh-018 now because of this. no more than once a week. comes and goes.
i do not smoke other than cannibinoid blends, or cannibis. am in good shape, excersise & running seemed to make it feel better usually, so i came to the conclusion it is not in fact my heart or lungs, but what is it exactly i have no clue.
i can't say for sure that is was jwh-018 even, only that smoking blends made the pain much worse, and cutting way back on the smoking blends made it much more mild, although it has not disappeared completely.