Figure (6).

A: Examples of effects of a specific Na⁺ channel blocker saxitoxin (STX) on AP duration, contraction and Ca²⁺ transient in ventricular cardiomyocytes of dogs with chronic heart failure at a low pacing rate of 0.2 Hz STX reduces AP duration, abolishes “dome” phase of contraction and of Ca²⁺ transient in failing cells. B: At higher pacing rates a specific I_NaL blockers ranolazine reduces diastolic tension, and a specific Na⁺ channel blocker tetrodotoxin (TTX) reduces Ca²⁺ accumulation (Fluo-4 signals). Adapted from [14, 15, 17], used with permission.