PAK1 and cardiac arrhythmia: In parallel with Pak1 action in SAN myocytes, enhanced Pak1 function brought about by Pak1 activating peptide, PAP (Wang et al., 2014b) in ventricular tissue prevented hypertrophic associated ventricular arrhythmias, and Pak1 deletion in Pak1cko or in knockout mice increased the risks of ventricular alternans and arrhythmias compared to WT mice.