The human KCNH2 gene encodes the pore-forming subunit of Kv11.1, the voltage-gated hERG potassium channel. HERG channels are upregulated in some types of cancer and may serve as a tumor marker. KCNH2 mutations cause inherited forms of cardiac disorders including both long QT (loss-of-function) and short QT (gain-of-function) syndromes. Inhibition of HERG channels by pharmaceuticals is the primary cause of acquired long QT syndrome and drug-induced torsade de pointe. Therefore, HERG is an anti-target in cardiac risk assessment.