Heart Conduction System (Cardiac Conduction)

What is the conduction system of the heart?

Your heart’s conduction system is the network of nodes (groups of cells that can be either nerve or muscle tissue), specialized cells and electrical signals that keep your heart beating.

Two types of cells control your heartbeat:

• Conducting cells carry the electric signals.
• Muscle cells control your heart’s contractions.

Your heart (cardiac) conduction system sends the signal to start a heartbeat. It also sends signals that tell different parts of your heart to relax and contract (squeeze). This process of contracting and relaxing controls blood flow through your heart and to the rest of your body.

What are the steps of the heart conduction pathway?

Your heart is a pump that sends blood through your body. For each heartbeat, electrical signals travel through the conduction pathway of your heart. It starts when your sinoatrial (SA) node creates an excitation signal. This electrical signal is like electricity traveling through wires to an appliance in your home.

The excitation signal travels to:

1. Your atria (top heart chambers), telling them to contract.
2. The atrioventricular (AV) node, delaying the signal until your atria are empty of blood.
3. The bundle of His (center bundle of nerve fibers), carrying the signal to the Purkinje fibers.
4. The Purkinje fibers to your ventricles (bottom heart chambers), causing them to contract.

These steps make up one full contraction of your heart muscle. Your heart conduction system sends out thousands of signals per day to keep your heart beating.

How does electrical conduction perform with the rest of your heart?

The electrical signals that travel through your heart conduction system cause your heart to expand and contract. These contractions control how blood flows through your heart.

Ideally, the electrical conduction system keeps up a steady, even heart rate. It also helps your heart speed up when you need more blood and oxygen or slow down when it’s time to rest.

What are the parts of the cardiac conduction system?

Your cardiac conduction system contains specialized cells and nodes that control your heartbeat. These are the:

• Sinoatrial node.
• Atrioventricular node.
• Bundle of His (atrioventricular bundle).
• Purkinje fibers.

Sinoatrial node

Your sinoatrial node is sometimes called your heart’s natural pacemaker. It sends the electrical impulses that start the heartbeat.

The SA node is in the upper part of your heart’s right atrium. It is at the edge of your atrium near your superior vena cava (vein that brings oxygen-poor blood from your body to your heart).

Your autonomic nervous system controls how fast or slowly your SA node sends electrical signals. This part of the nervous system directs hormones that control your heart rate based on what you are doing. For example, your heart rate increases during exercise and slows when you are asleep.

The autonomous nervous system includes your:

• Sympathetic nervous system (fight or flight response) makes your SA node work faster, which increases your heart rate.
• Parasympathetic nervous system (rest and digest response) makes your SA node work slower, which decreases your heart rate.

Atrioventricular node

The atrioventricular node delays the SA node’s electrical signal. It delays the signal by a consistent amount of time (a fraction of a second) each time.

The delay ensures that your atria are empty of blood before the contraction stops. The atria are the heart’s upper chambers. They receive blood from your body and empty it into the ventricles.

Your AV node is located in an area known as the triangle of Koch (located between the septal leaflet of the tricuspid valve, the coronary sinus and the membranous portion of the interatrial septum). This is near the central area of the heart.

Bundle of His

The bundle of His is also called the atrioventricular bundle. It is a branch of fibers (nerve cells) that extends from your AV node. This fiber bundle receives the electrical signal from the AV node and carries it to the Purkinje fibers.

The bundle of His runs down the length of the interventricular septum, the structure that separates your right and left ventricles. The bundle of His has two branches:

• Left bundle branch sends electrical signals through the Purkinje fibers to your left ventricle.
• Right bundle branch sends electrical signals through the Purkinje fibers to your right ventricle.

Purkinje fibers

The Purkinje fibers are branches of specialized nerve cells. They send electrical signals very quickly to your right and left heart ventricles.

Your Purkinje fibers are in the subendocardial surface of your ventricle walls. The subendocardial surface is part of the endocardium, the inner layer of tissue that lines your heart’s chambers.

When the Purkinje fibers deliver electrical signals to your ventricles, the ventricles contract. As they contract, blood flows from your right ventricle to your pulmonary arteries and from your left ventricle to your aorta. The aorta is the body’s largest artery. It sends blood from your heart to the rest of your body.

What conditions and disorders affect electrical conduction in your heart?

Several different conditions can affect your heart’s electrical system. These problems cause issues with your heart’s rhythm.

Some common heart rhythm disorders include:

• Arrhythmia: Irregular heart rhythm, including atrial fibrillation (Afib).
• Bundle branch block: A block in the Purkinje fibers on one side of your heart, causing arrhythmia.
• Heart block: Impaired electrical signals between your heart’s atria and ventricles.
• Long Q-T syndrome (LQTS): Your ventricles contract and release too slowly, sometimes leading to fainting (syncope) or sudden cardiac arrest.
• Premature ventricular contractions: A too-early heartbeat in your ventricles, causing heart palpitations or a “skipped heartbeat.”
• Sudden cardiac arrest: A severe malfunction in your heart’s rhythm that causes your heart to stop, resulting in death if not treated immediately.

How can I keep my heart conduction system healthy?

Many problems with heart rhythm are the result of genetic factors. They may be related to your heart’s structure or other factors.

But you can work to keep your cardiac conduction system and your entire heart well by living a healthy lifestyle. You may:

• Achieve and maintain a healthy weight.
• Avoid secondhand smoke and quit smoking.
• Don’t misuse drugs or prescription medications.
• Drink alcohol only in moderation.
• Eat a nutritious diet full of fruits, vegetables and whole grains.
• Exercise aerobically for at least 150 minutes per week.
• Manage stress with healthy coping techniques, such as talk therapy or meditation.

What else should I ask my doctor?

You may want to ask your healthcare provider:

• What are the symptoms of a heart conduction problem?
• What is the most likely cause of symptoms?
• Do I need to make lifestyle changes to improve my heart health?
• What tests do I need to check my heart health?

A note from Cleveland Clinic

Your heart’s conduction system is the network of signals that keeps your heart beating. These electrical signals make your heart contract or relax. Each contraction also controls blood flow through your heart. You can keep your heart conduction system and your entire heart healthy by making lifestyle changes such as managing stress and exercising regularly.