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Bundle branch block

Medically reviewed by Last updated on Jun 11, 2022.


Bundle branch block is a condition in which there's a delay or blockage along the pathway that electrical impulses travel to make the heart beat. It sometimes makes it harder for the heart to pump blood to the rest of the body.

The delay or blockage can occur on the pathway that sends electrical impulses either to the left or the right side of the bottom chambers (ventricles) of the heart.

Bundle branch block might not need treatment. When it does, treatment involves managing the underlying health condition, such as heart disease, that caused bundle branch block.

Bundle branch block

Electrical impulses that cause your heart to beat (contract) start in the heart's upper right chamber (right atrium) and travel to the lower chambers (ventricles). In bundle branch block, the pathway these impulses follow is delayed or blocked. The pathway includes two branches the left and the right bundles. If one bundle is damaged, the ventricles rely on the other bundle to receive and respond to signals from the right atrium. If both bundles are blocked, the heart may beat very slowly, which can require a pacemaker.


In most people, bundle branch block doesn't cause symptoms. Some people with the condition don't know they have bundle branch block.

Rarely, symptoms of bundle branch block may include fainting (syncope) or feeling as if you're going to faint (presyncope).

When to see a doctor

If you've fainted, see a health care provider to rule out serious causes.

If you have heart disease or have been diagnosed with bundle branch block, ask your provider how often you should have follow-up visits.


Electrical impulses within the heart muscle cause it to beat (contract). These impulses travel along a pathway, including two branches called the right and the left bundles. If one or both of these branch bundles are damaged — due to a heart attack, for example — the electrical impulses can become blocked. As a result, the heart beats irregularly.

The cause for bundle branch blocks can differ depending on whether the left or the right bundle branch is affected. Sometimes, there is no known cause.

Causes can include:

Left bundle branch block

Right bundle branch block

Risk factors

Risk factors for bundle branch block include:


If both the right and the left bundles are blocked, the main complication is a complete blockage of the electric signaling from the upper to the lower chambers of the heart. The lack of signaling can slow the heart rate. A slowed heart rate may lead to fainting, irregular heart rhythms and other serious complications.

Because bundle branch block affects the electrical activity of the heart, it can sometimes complicate the accurate diagnosis of other heart conditions, especially heart attacks. It may lead to delays in proper management of those heart conditions.


If you have a right bundle branch block and you're otherwise healthy, you might not need a full medical checkup. If you have a left bundle branch block, you will need a thorough medical exam.

Tests that can be used to diagnose a bundle branch block or its causes include:


Most people with bundle branch block don't have symptoms and don't need treatment. For example, left bundle branch block is not treated with medications. However, treatment depends on the specific symptoms and other heart conditions.


If you have a heart condition causing bundle branch block, treatment might involve medications to reduce high blood pressure or reduce symptoms of heart failure.

Surgeries and other procedures

If you have bundle branch block and a history of fainting, your health care provider might recommend a pacemaker. A pacemaker is a small device implanted under the skin of the upper chest. Two wires connect it to the right side of the heart. The pacemaker releases electrical impulses when needed to keep the heart beating regularly.

If you have bundle branch block with low heart-pumping function, you may need cardiac resynchronization therapy (biventricular pacing). This treatment is similar to having a pacemaker implanted. But you'll have a third wire connected to the left side of your heart so the device can keep both sides in proper rhythm. Cardiac resynchronization therapy helps the heart's chambers squeeze (contract) in a more organized and efficient way.

Preparing for your appointment

You're likely to start by seeing your primary care doctor. You might be referred to a doctor trained in heart disorders (cardiologist).

Here's some information to help you get ready for your appointment.

What you can do

Be aware of pre-appointment restrictions. When you make the appointment, ask if there's anything you need to do in advance. For example, you may need to limit or avoid caffeine before having heart function tests.

Make a list of:

Ask a family member or friend to come with you, if possible, to help you remember the information you receive.

For bundle branch block, questions to ask your provider include:

What to expect from your doctor

Your health care provider is likely to ask you questions, including:

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