Electrical System

The heart’s electrical system is responsible for making and conducting signals that trigger the heart to beat. These signals

The Electrical System Click the image to view an animation on the Electrical System

cause the heart’s muscle to contract. With each contraction, blood is pumped throughout the body. The process begins in the upper chambers of the heart (atria), which pump blood into the lower chambers (ventricles). The ventricles then pump blood to the body and lungs. This coordinated action occurs because the heart is "wired" to send electrical signals that tell the chambers of the heart when to contract.

The Heartbeat

Most of the time, you may not be aware of your heartbeat. When running up and down a flight of stairs, you may notice the pulse in your neck, chest, or wrist becomes strong and rapid. Your heartbeat is able to speed up and slow down because it can be influenced by the nerves and chemicals in the body and is wired with electrical tissue, similar to the wires that connect a stereo. Your heart also has its own "pacemakers" that are like electrical outlets. They send signals that tell the heart muscles to contract. This happens 24 hours a day, 365 days a year without rest, even when you do not notice.

Without the electrical system, the heart would not contract and would not pump blood. Blood would not circulate and the body would not receive the oxygen and nutrients it needs. When blood flow stops to the brain, a person loses consciousness in seconds and death follows within minutes.

How the Heart is Wired

You may know or have heard of someone with an artificial pacemaker or other implantable device to regulate the beat of the heart. Pacemakers and the wiring that run through the heart coordinate contractions in the upper and lower chambers, which makes the heartbeat more powerful so it can do its job most effectively.

We normally have our own natural pacemakers that tell the heart when to beat. The master pacemaker is located in the right atrium (upper chamber). It acts like a spark plug that fires in a regular, rhythmic pattern to regulate the heart's rhythm. This "spark plug" is called the sinoatrial (SA), or sinus node. It sends signals to the rest of the heart so the muscles will contract.

First, the atrium contracts. Like a pebble dropped into a pool of water, the electrical signal from the sinus node spreads through the atria. Next, the signal travels to the area that connects the atria with the ventricles, the atrioventricular node (AV node). This electrical connection is critical. Without it, the signal would never reach the ventricles, the major pumping chambers of the heart.

As the signal continues and crosses to the ventricles, it passes through another bundle of special electrical tissue called the Bundle of His. The Bundle then divides into thin, wire-like structures called the right and left bundle branches which extend into the right and left ventricles. The electrical signal next travels down the bundle branches to thin electrical fibers. Lastly, these fibers send out the signal to the muscles of the ventricles, causing them to contract and pump blood into the arteries. 

At rest, in a normal heart, this coordinated series of electrical signals occurs about once every second, maintaining the steady, rhythmic pattern of the heart’s beat and causing a normal pulse rate of 60 beats per minute.