Normal Heart Beat

1. The SA node sets the rate and rhythm of your heartbeat.

2. The SA node fires an impulse. The impulse spreads through the walls of the right and left atria, causing them to contract. This forces blood into the ventricles.

3. The impulse travels to the AV node. Here, the impulse slows for a moment before going on to the ventricles.

4. The impulse travels through a pathway of fibers called the HIS-Purkinje network. This network sends the impulse into the ventricles and causes them to contract. This forces blood out of the heart to the lungs and body.

5. The SA node fires another impulse. The cycle begins again.