Arrhythmogenic mechanisms of CaMKIIδC-mediated INa regulation. Gain (+) and loss (−) of function effects of CaMKIIδC phosphorylation are indicated with upward and downward triangles, respectively. NCX, Na/Ca exchanger; NKA, Na-K-ATPase; NaV1.5, voltage-gated Na channel isoform 1.5; RyR, ryanodine receptor; PLB, phospholamban; SERCA, sarco(endo)plasmic reticulum Ca ATPase; APD, AP duration.