hERG (human ether-a-go-go-related gene) encodes the alpha subunit of a potassium ion channel, Kv11.1. It contains six transmembrane α-helices with a re-entrant “poreloop” between the fifth and the sixth transmembrane helices. This ion channel is best known for its contribution to the electrical activity of the heart that coordinates the heart's beating. When this channel's ability to conduct electrical current across the cell membrane is inhibited or compromised, either by application of drugs or by rare mutations, it can result in a potentially fatal disorder called long QT syndrome. A number of clinically successful drugs in the market exhibit the potential to inhibit hERG, and create a concomitant risk of sudden death as a side-effect, which has made hERG inhibition an important off-target that must be avoided during drug development.