Binds specifically to voltage-gated sodium channels (Nav), thereby delaying their inactivation during signal transduction. Thus it strongly stimulates mammalian cardiac muscle contraction. Belongs to the sea anemone sodium channel inhibitory toxin family. Type I subfamily. Opinions are divided on whether Anemonia viridis (Forsskal, 1775) and Anemonia sulcata (Pennant, 1777) are separate species.