Your Heart's Electrical SystemThe heartbeat is the rhythmic contraction of the heart muscle's 4 chambers. The heart muscle has a special system that creates and sends electrical signals to activate these 4 chambers. First, a signal generated in the right upper chamber of the heart tells the 2 upper chambers (atria) to squeeze. This moves blood to the 2 lower chambers (ventricles). Next, electrical signals tell the ventricles to squeeze. This moves blood to the lungs, brain, heart, and body.
Groups of special cells in the right atrium, called nodes, send out the heart's electrical signals. The signals travel along pathways. In the ventricles, these pathways are called bundle branches.
The SA (sinoatrial) node
This sets the pace of the heartbeat. It starts each beat by releasing a signal telling the atria to squeeze.
The AV (atrioventricular) node
This receives the signal from the atria. It is the "gateway" between the atria and the ventricles. The AV node channels the signal into the ventricles.
The Bundle branches
These carry the signal through the ventricle walls. As the signal moves through the ventricles, the ventricles squeeze.