Anthopleurin is a toxin from the venom of the sea anemones Anthopleura xanthogrammica and Anthopleura elegantissima. These anemones use anthopleurin as a pheromone to quickly withdraw their tentacles in the presence of predators. Anthopleurin has four isoforms (Anthopleurin-A, -B, -C, and -Q). Their working mechanism is based on binding to sodium channels, which leads to increased excitation especially in cardiac myocytes.