Figure1: Scheme of the moment that the If pacemaker current acts during P cell potential (Phase 4). SAN cells characteristics. Typical profile of APs of slow fibers, which are found in the SAN, AVN and mitro-tricuspid rings. It is characterized by having lower amplitude, absence of identifiable phase 1 and 2, and phase 4 with significant slope (automatism, rhythmycity or phase 4 diastolic despolarization). In the minor left inferior figure is represented the moment of action of If, ICa-T, and ICa-Lon phase 4.