Synthetic cannabinoid, JWH-030, induces QT prolongation through hERG channel inhibition †Electronic supplementary information (ESI) available. See DOI: 10.1039/c6tx00259e The problem of new psychoactive substance (NPS) abuse, which includes synthetic cannabinoids, is emerging globally, and the cardiotoxicity of these synthetic cannabinoids has not yet been evaluated extensively. In the present study, we investigated the effects of synthetic cannabinoids on the cytotoxicity, human Ether-à-go-go-related gene (hERG) channel, action potential duration (APD), and QT interval. The 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay showed that JWH-030 was more cytotoxic than JWH-210, JWH-250, and RCS4 in H9c2 cells at 0.1 μM. In addition, the cytotoxicity was associated