Consequently, mutations within the SCN5A gene encoding for Nav1.5 have been linked to the sick sinus syndrome (Benson et al., 2003; Lei et al., 2008), cardiac conduction defects (Schott et al., 1999; Lei et al., 2008), and different forms of arrhythmias (Bezzina et al., 1999; Darbar et al., 2008). This evidence concerns the gene SCN5A and sick sinus syndrome.