The movement of electrical signals across the heart is what is traced on an electrocardiogram (EKG). The EKG is also what allows irregularities in the heart’s electrical system, and with them any related symptoms and medical conditions, to be assessed.

This article explains five components of the cardiac conduction system and how they work. It also discusses how heart disease or a heart attack can cause serious disruptions in the system.

The cardiac electrical signal controls the heartbeat in two ways. First, since each electrical impulse generates one heartbeat, the number of electrical impulses determines the heart rate. In a normal sinus rhythm, that rate will be between 60 and 100 beats per minute.

The sinus node signal also controls electrical conduction as it “spreads” across the heart. It causes the cells of the heart muscle to contract in the correct sequence, and ensures regular, efficient, and coordinated heartbeats. For this reason, the sinus node is often referred to as the heart’s “natural pacemaker.”

In this figure:

SN = sinus nodeAVN = AV nodeRA = right atriumLA = left atriumRV = right ventricleLV = left ventricleTV = tricuspid valve (the valve that separates the right atrium from the right ventricle)MV = mitral valve (the valve that separates the left atrium from the left ventricle)

As the electrical impulse passes through the atria, it generates the so-called “P” wave on the EKG. The P wave is indicated by the solid red line on the EKG in the left side of the image above.

This pause allows the atria to contract fully, emptying blood into the ventricles before the ventricles begin to contract.

The right and left bundle branches, in turn, send the electrical impulse to the right and left ventricles, respectively. The figure also shows that the LBB itself splits into the left anterior fascicle (LAF) and the left posterior fascicle (LPF).

In this manner, the electrical system of the heart causes the heart muscle to contract and send blood to the organs of the body (via the left ventricle) and to the lungs (via the right ventricle).

In most cases of heart block, the electrical signals are weakened but do not stop completely. There are three degrees of heart block severity:

First degree heart block: The least severe degree of heart block, in which the electrical signals are slowed but still reach your ventricles. Treatment may not be needed. Second degree heart block: The heart’s electrical signals are irregular, causing the heart to occasionally skip a beat. A pacemaker may be considered. Third degree heart block: The most severe degree of heart block, in which electrical signals completely fail to reach the ventricles. If this happens, a person’s pulse may dramatically slow, or there may be no pulse at all. A pacemaker is almost always required.

Another type of conduction disorder, bundle branch block, occurs when a blockage in the right or left bundle branch causes one ventricle to contract slightly slower than the other. This results in an irregular heartbeat (arrhythmia).

Bundle branch block by itself often does not require treatment. When it does, treatment involves managing the underlying health condition, be it heart disease, high blood pressure, a congenital (present at birth) heart defect, or something else.

Having a conduction disorder, in which the heart’s electric pathway is disrupted, increases the risk of major complications, including cardiac arrest. Fortunately, there are ways to reduce your risk of a conduction disorder or related complications, including regular exercise and a heart-healthy diet.