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Normally, electrical impulses within your heart's muscle signal it to beat (contract). These impulses travel along a pathway, including the right and the left bundles. If one or both of these branch bundles become damaged — due to a heart attack, for example — this change can block the electrical impulses and cause your heart to beat abnormally.

The underlying cause for bundle branch blocks may differ depending on whether the left or right bundle branch is affected. It's also possible that this condition can occur without any known underlying cause. Specific causes may include:

Left bundle branch block

  • Heart disease
  • Thickened, stiffened or weakened heart muscle (cardiomyopathy)
  • A viral or bacterial infection of the heart muscle (myocarditis)
  • High blood pressure (hypertension)

Right bundle branch block

  • A heart abnormality that's present at birth (congenital) — such as atrial septal defect, a hole in the wall separating the upper chambers of the heart
  • A heart attack (myocardial infarction)
  • A viral or bacterial infection of the heart muscle (myocarditis)
  • High blood pressure (hypertension)
  • A blood clot in the lungs (pulmonary embolism)
April 10, 2015