Normal Conduction System
The sinus node (sinoatrial node or SA node) is the heart's own pacemaker. The electrical impulse is normally initiated here. The impulse travels across the atria (top 2 collecting chambers) stimulating contraction or "squeeze" and will eventually push blood into the ventricles (the bottom 2 pumping chambers).
The impulse then reaches the AV node (atrioventricular node). This is referred to as the "gateway" to the ventricles. The AV node receives the impulse from the SA node.
The impulse moves through special electrical tissue starting at the Bundle of His, moving to the bundle branches. This stimulates ventricular squeeze, which pumps blood to the lungs and the rest of the body. Each of these cycles is a "heart beat". Below is a picture of cardiac conduction system.
Normal heart rate varies in children based on age. Infants and children have a faster heart rate compared to adults. The normal adult heart rate is 60-100 beats per minute