The cardiac impulse originates in a relatively small group of primary pacemaker cells . typical primary pacemaker cells have the highest intrinsic frequency in firing . following its firing , there is a slow depolarization called pacemaker potential 位于右心房竇房結內的起搏細胞具有最高的固有發放節律,每次發放后即出現一個緩慢的自動去極化過程,心率主要取決于起搏細胞去極化的斜率。