Specifically, JNK2 increases diastolic SR Ca2+ leak via CaMKIIδ-dependent phosphorylation of RyR2, which sensitizes RyR2 channels, triggers aberrant Ca2+ waves, prolongs the intracellular Ca2+ decay time constant, enhances spatiotemporal heterogeneity of Ca2+ and electrical impulses, and augments AF susceptibility. This evidence concerns the gene MAPK9 and atrial fibrillation.