To make a heartbeat, an electrical signal is generated by the heart's sinus node, which is a small mass of specialized tissue located in the right upper chamber of the heart. The signal makes the heart beat roughly 60-190 times per minute, depending on the age and activity level of the child.
This electrical signal travels to the heart similar to the way electricity flows through power lines, from the power plant to your house. The signal causes the heart's chambers to contract and pump out blood. This "electricity" can be measured by a test called an electrocardiogram.
The electrical impulse travels from the sinus node to the atrioventricular (AV) node, where impulses are slowed down for a very short period, and then continues down the conduction pathway into the ventricles. The signal is split to divide into right and left pathways to provide electrical stimulation to both ventricles. Any tissue that controls the frequency of the heartbeats is called a pacemaker.
The right and left atria (the two upper chambers of the heart) are stimulated first and contract a short period of time before the right and left ventricles (the two lower chambers of the heart). The closure of the heart valves after contraction produces the heart's thumping sound. Each contraction represents one heartbeat.
Under some conditions, almost any heart tissue is capable of starting a heartbeat or becoming the “pacemaker” and acting like the sinus node.
Abnormalities in the heart’s electrical system can cause a heart to beat too quickly, too slowly or irregularly. These variations in heart rhythm are called arrhythmia. People with arrhythmia can have the normal pace of their heartbeat restored through electric shock from an automated external defibrillator (AED).