Given the conclusions of DeSantiago et al. [18] regarding PAK1 activation as a protection against NCX-induced arrhythmias, we tested the transcriptional activation of Slc8a (Ncx) isotypes in Pak1fl/fl and Pak1 cKO mouse atria in the presence and absence of ISO to investigate whether the CamkIIδ/Creb1 pathway induces Slc8a expression. The gene discussed is CREB1; the disease is Arrhythmia.