Structures involved in inactivation within the Nav1.5 α-subunit. Structures colored in red significantly affect fast inactivation. From N-terminal to C-terminal, the intracellular end of DI S6 segment (ΔWCW window),45,47 intracellular end of DII S6 segment,45 DIII S4-S5 linker,38,39,42 DIII-DIV linker,25-33 DIV S4-S5 linker,40-42 lower half of DIV S6 segment,44,47 and C-terminus.23,48-51,53