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.

This sets the pace of the heartbeat. It starts each beat by releasing a signal telling the atria to squeeze.

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.

These carry the signal through the ventricle walls. As the signal moves through the ventricles, the ventricles squeeze.