 It has been suggested that some of these effects may be mediated by serotonergic neurotoxicity/depletion of serotonin with chronic administration and/or activation of serotonin 5-HT2A receptors.The distinctive valvular abnormality seen with fenfluramine is a thickening of the leaflet and chordae tendineae.One mechanism used to explain this phenomenon involves heart valve serotonin receptors, which are thought to help regulate growth.