Binds specifically to voltage-gated sodium channels (Nav) (site 3), thereby delaying their inactivation during signal transduction (By similarity). Has a heart stimulation effect on isolated rat atria that is higher than that of Hk7a, Hk8a and Hk16a (PubMed:12782079,PubMed:14672713). LD(50) is 1.4 mg/kg when intraperitoneally injected into mice. Belongs to the sea anemone sodium channel inhibitory toxin family. Type I subfamily.