Control of the Heart Beat

1. The sinoatrial (SA) node is the pacemaker of the heart. Located in the wall of the right atrium, it initiates the impulse that starts each heart beat.

2. The impulse spreads through the walls of the atria causing their cardiac muscle cells to contract. This produces atrial systole.

3. The antrioventricular (AV) node collects the impulse and sends it down through the atrioventricular (AV) bundle.

4. The left and right atrioventricular (AV) bundles carry the impulse down through the interventricular septum to the Purkinje fibers.

5. The Purkinje fibers receive the impulse from the AV bundle at the apex of the heart and spread it up the ventricular walls causing their cardiac muscle cells to contract. This produces ventricular systole.