The natural pacemaker of the heart is the Sinoatrial Node . It is located above the right atrium near the opening of the superior vena cava.
The sinoatrial node generates rhythmical impulses first then it is relayed into the atrioventricular node located between the atrium and ventricle of the heart. In here, the impulses are delayed to allow blood from the atrium to fill into the ventricles. Impulses again are relayed to the left and right bundle branches of the Purkinjie fibers which conduct cardiac impulses throughout the parts of the left and right ventricles.