To beat properly, the heart’s tissue conducts electrical impulses throughout the muscle in a regular pattern. However, if an area of this pattern is blocked near the heart’s ventricles, the electric impulse must travel slightly longer to reach its endpoint. This makes it harder for the heart to pump blood throughout your body.

Doctors call the resulting electrical pattern bundle branch block because the electrical impulse encounters a roadblock at the left or right branch of the “bundle of His.” The bundle of His is an area of the heart that conducts impulses to the left and right ventricles.

Left bundle branch block (LBBB) is a blockage of electrical impulses to the heart’s left ventricle. This is the lower-left portion of the heart.

LBBB doesn’t always cause symptoms. In fact, some people have it for years and never know it. For others, however, a delay in the arrival of electrical impulses to the heart’s left ventricle can cause syncope, which is fainting due to unusual heart rhythms that affect blood pressure.

Some people might also experience something called presyncope. This involves feeling like you’re about to faint, but never actually fainting.

According to the Texas Heart Institute, a bundle branch block on the left may also increase your risk of developing heart disease.

A variety of things can cause LBBB. For example, a heart attack can damage your heart tissue, making it harder for it to conduct electricity. This can result in bundle branch block at either the right or left ventricle.

Other conditions that can cause an LBBB include:

While anyone can develop LBBB, some people have a higher risk due to other conditions that affect their heart or lungs.

Conditions that can increase your risk of bundle branch block on either the left or right side include:

If you have any of these conditions, your doctor might regularly monitor your heart rhythm to detect any signs of bundle branch block.

Doctors usually diagnose LBBB by using an electrocardiogram (EKG). This is a painless test that involves placing stickers called leads around your chest. The leads conduct electricity. They’re connected to wires that sense the electrical impulses of your heart and trace your heart’s rhythm.

Sometimes, a bundle branch block makes it harder for doctors to diagnose other heart conditions, such as heart failure or enlargement. If you’ve been diagnosed with LBBB, make sure to tell any other doctors you see that you have one.

LBBB doesn’t always require treatment, especially if you don’t have any underlying heart conditions. If you do have another heart condition, your doctor might suggest treating the underlying cause.

If you have LBBB due to a heart attack, for example, you may need a pacemaker. This is a device that emits electricity to help your heart maintain a consistent rhythm.

If you have high blood pressure, you may need to take medication to keep it under control. This will also reduce the strain on your heart.

While treating the underlying condition might not completely get rid of LBBB, it can lessen the severity of it and prevent future damage.

LBBB can seem alarming, but they’re usually not as serious as they sound. In some cases, you might not even know you have one. If you have LBBB that needs treatment, your doctor will come up with a plan that addresses the underlying cause.