Heart Electrical System Anatomy and Sequence of Electrical Conduction

The heart sequence of electrical conduction starts in the upper-right wall of the right atrium where specialized cells form a cluster called the sinoatrial (SA) node. The SA node is known as the heart’s pacemaker and it creates the starting signal for each heartbeat. When the SA node triggers an electrical pulse, it sends electrical messengers racing toward left atrium and toward the second important cell cluster, called the atrioventricular (AV) node. The AV node is located in the lower-left side of the right atrium and the electrical activity between the SA and AV segment of the race causes the muscles of both the left and right atria to contract, which helps push blood from the atria into the ventricles. 

After a brief rest to allow the ventricles to fill with blood, the electrical baton is handed from the AV node to a narrow group of Purkinje cells called the bundle of His. From here, the electrical racers split off in two directions: half head down the track toward the right ventricle and the other half race toward the left ventricle. The final hand-off occurs at the base of the ventricles, where the electrical impulse is sent through thin Purkinje fibers on both sides of the heart. The final sprint through the Purkinje fibers causes the muscular walls of the ventricles to contract, which pumps blood from the right ventricle into the lungs and from the left ventricle out into the body. At this point, the heartbeat is complete and the electrocardio relay race starts up again from the SA node.

 You can think of the heart’s electrical conduction system as an electric relay race, where the electrical baton is passed between groups of cells that make different regions of the heart contract at different times.



Each heartbeat is created by muscle contractions that squeeze the chamber walls in a precise pattern. These muscle contractions provide the force that pumps blood throughout your body, similar to a foot pump that forces air into your favorite floating device. But instead of pumping air into toys for a pool party, your heart functions as a dual blood pump to support your life party. The “dual” part of the blood pump arises because the right and left sides of your heart function as separate pumps that send blood to two different destinations: the lungs and the body. The right chambers of your heart receive deoxygenated blood from your body’s veins and pump it into your lungs and the left chambers of your heart pump the recently oxygenated blood into the rest of your body.

A heart arrhythmia occurs when a heart is beating too fast, too slow, or when there is a problem with a heart’s pattern of refill and pump. A person can be born with an irregular heartbeat, but arrhythmias can also occur when damaged or aging heart tissue prevents electrical signals from making smooth and properly paced laps around the electrocardio racetrack. The fact that the heart has a self-contained electrical system has allowed for the development of useful medical treatments, such as the defibrillator and the artificial pacemaker. Both of these devises can help a patient whose heartbeat has an irregular rate or rhythm.

Most arrhythmias are not life-threatening. However, if an irregular heartbeat impairs the pumping of blood into the lungs and the rest of the body, it can have immediate and deadly consequences. The cells in the human body require a constant supply of oxygen and if the heart’s chambers are not contracting at the right times or if they are not contracting strongly enough, it can result in a dangerous decrease blood flow and oxygen delivery. Without proper oxygen delivery, a person can pass-out and die within minutes. Therefore, it is essential that you pay attention to your blood pump and seek immediate medical care if you sense an abnormality in your heartbeat’s rate or rhythm.

Heart Sequence of Electrical Conduction: Electrical signals move from the sinoatrial (SA) node to atrioventricular (AV) node in the atria, then move to a narrow group of Purkinje cells called the bundle of His and finally move to the Purkinje fibers in the left and right ventricles.

Heart Arrhythmias: Heartbeat with an irregular rate or rhythm.

Pacemaker: Device that detects irregular heart contractions and then send electrical pulses to override and correct the abnormality with each heartbeat.

Electrocardiogram (ECG or EKG): Tool that detects the heart’s electrical sequence of electrical conduction.