The heart has two upper chambers called atria and two lower chambers called ventricles. Electrical signals move through special nerve bundles to the atria then to the ventricle. When the electrical signals pass through as expected the heart pumps rhythmically.

Heart block occurs when the electrical signals do not travel normally through the heart. The heart can still pump blood but it beats much slower and less efficiently than normal. There are three types of heart block, ranging from mild to serious:

  • First-degree heart block—mildest form of heart block. Electrical signals reach all parts of the heart but move more slowly than normal. There are usually no symptoms, and heartbeat is normal.
  • Second-degree heart block—some of the electrical signals are not reaching the ventricles. This means sometimes the ventricles do not pump when they should.
  • Third-degree, or complete, heart block—most serious type of heart block. No electrical signals are able to reach the ventricles. Cells in the ventricles act as a back up and create their own electrical signals. This allows the ventricles to keep pumping but it is slower and out of rhythm with the rest of the heart. .

Anatomy of the Heart
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The causes of heart block in children may include:

  • Heart defect caused by genetics
  • Certain medications
  • Damage from surgery
  • Infections such as Lyme disease
  • Lupus in the mother
  • Electrolyte abnormalities
  • Autoimmune disorder