The piperazine derivative mCPP (a major metabolite of trazodone) is a 5-HT2B agonist in animal models, but actually behaves as a 5-HT2B antagonist in humans [REF].
One study of human users of MDMA ("ecstasy") found that they did have heart valve changes suggestive of early cardiac fibrosis, which were not present in non-MDMA using controls,[REF] suggesting that MDMA use certainly has the potential to cause this kind of heart damage.