Endocardial fibrosis has been associated with 5-HT2B activation and is therefore a potential adverse effect to consider for chronic use of substances interacting with this receptor (Rothman et al., 2000; Droogmans et al., 2007; Roth 2007; Doly et al., 2008; Elangbam et al., 2008; Bhattacharyya et al., 2009; Huang et al., 2009; Elangbam 2010; Dawson and Moffatt 2012). Here, HTR2B is linked to Endocardial fibrosis.