The human heart is an engine that has to work 24/7 to keep you alive, and it has to be reliable and effective. To do this, it relies on a specialized network of cells that conduct electricity to the different parts of your heart. This network is the heart’s electrical system.
The human heart is an engine that has to work 24/7 to keep you alive, and it has to be reliable and effective. To do this, it relies on a specialized network of cells called the cardiac conduction system. It’s also known as your heart’s electrical system.
Cells in the cardiac conduction system can generate electrical impulses and then distribute the signal throughout your heart. While all cells in your heart can conduct electricity, the cells in this system conduct it at very specific speeds. This is how different parts of your heart beat at just the right time. The parts of the cardiac conduction system are (in order, starting where electricity is generated):
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Your body uses electrical impulses to control when your muscles flex and relax, and your heart is no different. However, your heart needs to do this 24/7, whether you’re asleep or awake. To do this, it relies on a specific part of your nervous system called the autonomic nervous system. This is the unconscious part of your nervous system, and it runs the functions of your body that you don’t think about. This includes your heart, breathing, digestion and more.
The timing of your heart muscle’s action is also critical. Rather than your brain firing the electrical impulses, it relies on your heart’s conduction system. To do that, your brain sends signals through your autonomic nervous system to your heart’s electrical system. That system activates, sending an electrical pulse through your heart muscle. This makes the chambers of your heart squeeze in a specific order, creating a heartbeat.
Under normal circumstances, this happens between 50 to 100 times per minute when you're at rest. When you're active, your heart speeds up and beats faster.
Your body has three types of muscle: smooth, skeletal and cardiac.
Muscle Characteristics | Smooth muscle cells | Cardiac muscle cells | Skeletal muscle cells |
---|---|---|---|
How it’s controlled | Unconscious (without you thinking about it). | Unconscious. | Conscious (these move when you think about it). |
Shape | Wheel-shaped. More round when relaxed, oval-shaped when flexed. | Rectangular. Forms a mesh-like pattern with cells around it. | Long, fiber-like shape. |
Appearance | Distinct cells, each with one nucleus. | Distinct cells, each with one nucleus. Streaked across their width. | Cells form larger fibers with many nuclei. Streaked across their width. |
Speed of contraction | Slow. | Fast. | Variable. |
Timing of action | Repeating pattern. | Repeating pattern. | Upon command. |
Muscle Characteristics | |||
How it’s controlled | |||
Smooth muscle cells | |||
Unconscious (without you thinking about it). | |||
Cardiac muscle cells | |||
Unconscious. | |||
Skeletal muscle cells | |||
Conscious (these move when you think about it). | |||
Shape | |||
Smooth muscle cells | |||
Wheel-shaped. More round when relaxed, oval-shaped when flexed. | |||
Cardiac muscle cells | |||
Rectangular. Forms a mesh-like pattern with cells around it. | |||
Skeletal muscle cells | |||
Long, fiber-like shape. | |||
Appearance | |||
Smooth muscle cells | |||
Distinct cells, each with one nucleus. | |||
Cardiac muscle cells | |||
Distinct cells, each with one nucleus. Streaked across their width. | |||
Skeletal muscle cells | |||
Cells form larger fibers with many nuclei. Streaked across their width. | |||
Speed of contraction | |||
Smooth muscle cells | |||
Slow. | |||
Cardiac muscle cells | |||
Fast. | |||
Skeletal muscle cells | |||
Variable. | |||
Timing of action | |||
Smooth muscle cells | |||
Repeating pattern. | |||
Cardiac muscle cells | |||
Repeating pattern. | |||
Skeletal muscle cells | |||
Upon command. |
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Knowing the heart's structure helps in understanding your heart's electrical system. Your heart has four chambers. The upper chambers are the left atrium and right atrium (they’re called atria when you refer to them both). The lower chambers are the left and right ventricles.
Blood travels through your heart in the following steps (the steps on the left and right are happening at the same time):
As electricity moves through your heart, it causes each part it passes through to contract. This is called the electrical cascade. While all of the cardiac muscle in your heart can conduct electricity, there are certain areas of your heart — the electrical conduction system — where the cascade travels at different speeds.
The cascade travels through the electrical conduction system in the following order:
The sinoatrial (SA) node is a cluster of cells that act as a natural pacemaker for your heart. The SA node is located in a wall of the right atrium of your heart. This step is where the upper chambers of the heart begin to squeeze.
The atrioventricular (AV) node is located in the wall between the upper chambers of your heart. This node is very similar to the SA node but smaller, and electricity travels slower here. The slowing effect gives the ventricles enough time to expand and fill up with blood.
The Bundle of His (pronounced “hiss”) is a cluster of cells that extends outward from the AV node and travels down the center of your heart. Because these conduct electricity faster than surrounding tissue, it functions much like a lightning rod, directing the electrical cascade further into the heart.
The bundle branches are where the Bundle of His splits into two branches. The split happens at roughly the same level where the top and bottom chambers of the heart are divided. The branches carry the electrical cascade to the outer areas of the heart, especially the ventricles.
As the bundle branches fan out, they become a web-like network of conducting segments called the Purkinje fibers. The Bundle of His, bundle branches and Purkinje fibers are often described as the His-Purkinje system, which has a shape like an upside-down umbrella. The Bundle of His is the handle, the bundle branches are the stem and the Purkinje fibers are the umbrella's canopy.
Electricity travels down and then spreads out at the bottom of the heart. Electricity then travels upward and along the outer areas of the heart. This is how the heart pumps blood upward and out of the heart.
The heart conducts electricity in a specific way as described above, and its function works best when it maintains this sequence. Any time there is a disturbance of this sequence, it can cause abnormal heart rhythms and patterns called arrhythmias (irregular heart rhythms).
Arrhythmias mainly happen in two ways:
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The common symptoms of arrhythmia could include:
Many of these symptoms, especially chest pain, dizziness, syncope, palpitations or sudden shortness of breath are reasons that you need to seek emergency medical care.
A diagnostic tool called an electrocardiogram can analyze your heart’s electrical activity. Abbreviated as ECG or EKG, this is a test that measures your heart’s electrical activity using sensors attached to your chest. There are several ways to perform an EKG.
There are several ways to treat problems with your heart’s electrical system.
There are several actions you can take to help your heart’s health.
A note from Cleveland Clinic
The electrical conduction system of your heart is a key part of your survival, and it's one that runs automatically. Understanding how it works can help you spot potential problems and seek help. A healthcare provider can often recommend a wide range of treatments, from medications to minimally invasive surgeries, that can help treat or even cure electrical problems in your heart.
Last reviewed on 03/17/2022.
Learn more about the Health Library and our editorial process.
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Cleveland Clinic is a non-profit academic medical center. Advertising on our site helps support our mission. We do not endorse non-Cleveland Clinic products or services. Policy