Heart block is the delayed or complete lack of electrical communication between the upper chambers of the heart (atria) and the lower chambers of the heart (ventricles). Normally, the ventricles are stimulated to contract by electrical impulses that travel through the conduction system from the upper-right chamber of the heart to the ventricles. If these impulses are delayed as they travel to the ventricles, an abnormally slow heart rhythm (bradycardia) could result. If these impulses are completely blocked from reaching the ventricles, they will fail to stimulate a heartbeat at all. In this case, secondary impulses may arise in the ventricles (producing ventricular escape beats). However, if no secondary beats arise, this situation will result in death without immediate treatment.

Certain factors may contribute to heart block. They include:

In some cases, physicians may surgically induce heart block to treat the abnormal heartbeat known as atrial fibrillation. When atrial fibrillation cannot be controlled by other means, a cardiac electrophysiologist is able to ablate (destroy) the atrioventricular (AV) junction and induce complete heart block. The patient would then become dependent on a permanent pacemaker to govern the heartbeat in the lower chambers of the heart. Although this procedure is not a cure for atrial fibrillation, it prevents the rapid and irregular pulse associated with the condition and can be quite effective in reducing symptoms.