Cardiac conduction system

Everyone has a built-in electrical system in their heart that makes it beat, called the "cardiac conduction system." With each normal heartbeat, an electrical signal follows a path of special muscles called the "conduction pathway" across the heart. The signal starts in 1 spot near the top of the heart called the "SA node." From there, the signal travels to the "AV node" and then the rest of the heart. As it spreads, the signal makes the heart muscle squeeze. This pumps blood to the rest of the body.

When the electrical system is not working properly, it causes an abnormal heart rhythm, called an "arrhythmia."