Final answer:
The primary pacemaker of the heart is the SA node, which sets the normal rate of the heart's electrical activity.
Step-by-step explanation:
The primary pacemaker of the heart, which sets the normal rate, is the SA node (Sinoatrial Node). It is a small mass of specialized myocardial conducting cells located in the superior and posterior walls of the right atrium near the orifice of the superior vena cava. The SA node has the highest inherent rate of depolarization and determines the sinus rhythm or the normal electrical pattern followed by contraction of the heart.