SCN5A and Sinus bradycardia: Despite the lack of Nav1.5 channels in primary pacemaker cells, there is ample evidence that many SCN5A mutations are associated with inherited SAN dysfunction manifestations such as bradycardia and sinus-exit block and that symptomatic and asymptomatic sinus bradycardia is also often observed both in patients affected by Brugada or LQT3 syndrome (Table 1; Fig. 3b, c).