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What Causes Heart Block?

Heart block has many causes. Some people are born with the disorder (congenital), while others develop it during their lifetimes (acquired).

Congenital Heart Block

One form of congenital heart block occurs in babies whose mothers have autoimmune diseases, such as lupus. With autoimmune diseases, the body makes proteins called antibodies that attack and damage tissues or cells.

In pregnant women, antibodies can cross the placenta. (The placenta is the organ that attaches the umbilical cord to the mother's womb.) These proteins can damage the baby's heart and lead to congenital heart block.

Congenital heart defects also can cause congenital heart block. These defects are problems with the heart's structure that are present at birth. Often, doctors don't know what causes congenital heart defects.

Acquired Heart Block

Many factors can cause acquired heart block. Examples include:

Other diseases may increase the risk of heart block. Examples include sarcoidosis (sar-koy-DOE-sis) and the degenerative muscle disorders Lev's disease and Lenegre's disease.

Certain types of surgery also may damage the heart's electrical system and lead to heart block.

Exposure to toxic substances and taking certain medicines—including digitalis, beta blockers, and calcium channel blockers—also may cause heart block. Doctors closely watch people who are taking these medicines for signs of problems.

Some types of heart block have been linked to genetic mutations (changes in the genes).

An overly active vagus nerve also can cause heart block. You have one vagus nerve on each side of your body. These nerves run from your brain stem all the way to your abdomen. Activity in the vagus nerve slows the heart rate.

Sometimes acquired heart block will go away if the factor causing it is treated or resolved. For example, heart block that occurs after a heart attack or surgery may go away during recovery.

If medicine is causing heart block, the disorder may go away if the medicine is stopped or the dosage is lowered. (Always talk with your doctor before you change the way you take your medicines.)

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Heart Block Clinical Trials

Clinical trials are research studies that explore whether a medical strategy, treatment, or device is safe and effective for humans. To find clinical trials that are currently underway for Heart Block, visit

Know the Facts and Act Fast!

Collage image of new heart attack materials

When a heart attack happens, any delays in treatment can be deadly. 

Knowing the warning symptoms of a heart attack and how to take action can save your life or someone else’s.

The NHLBI has created a new series of informative, easy-to-read heart attack materials to help the public better understand the facts about heart attacks and how to act fast to save a life.

Click the links to download or order the NHLBI's new heart attack materials:

“Don’t Take a Chance With a Heart Attack: Know the Facts and Act Fast” (also available in Spanish)

“Heart Attack: Know the Symptoms. Take Action.”

“Learn What a Heart Attack Feels Like—It Could Save Your Life”

July 09, 2012 Last Updated Icon

The NHLBI updates Health Topics articles on a biennial cycle based on a thorough review of research findings and new literature. The articles also are updated as needed if important new research is published. The date on each Health Topics article reflects when the content was originally posted or last revised.