KCNH2 and cardiac rhythm disease: Trazodone, a serotonin modulator, rarely causes cardiac arrhythmias but is important to be aware of.11 High-dose trazodone inhibits all major cardiomyocyte ion channels (IKr, Iks, INa, and I Ca) through an especially high inhibitory potency human ether-a-go-go related gene (hERG).