RAPGEF4 and Arrhythmia: At the cellular level, EPAC regulates AP lengthening in rat ventricular cardiomyocytes (Brette et al., 2013), a process which is correlated with the genesis of arrhythmia by predisposing cardiomyocytes to early after depolarization and dispersion of repolarization (Nattel et al., 2007).