The authors see cisapride as a potent HERG blocker, active at levels reached in normal use. They wrote” could underlie QT prolongation and torsades de pointes.” They note the block is absent in closed channels but shifts with voltage once the channel is open or inactivated. The IC50 of 6.5nM lies within the therapeutic range, as they saw, yet most of the drug stays bound to plasma proteins, perhaps why QT changes are rarely seen. Still, when free levels rise through liver disease, drug interaction or overdose, the risk climbs. The authors see the work as a step closer to safer gut motility drugs and note a link with HERG type channels in myenteric plexus.