A genetic cardiac rhythm disease that may progress to complete atrioventricular (AV) block. The disease is either asymptomatic or manifests as dyspnea, dizziness, syncope, abdominal pain, heart failure or sudden death.

Syncope refers to a generalized weakness of muscles with loss of postural tone, inability to stand upright, and loss of consciousness. Once the patient is in a horizontal position, blood flow to the brain is no longer hindered by gravitation and consciousness is regained. Unconsciousness usually lasts for seconds to minutes. Headache and drowsiness (which usually follow seizures) do not follow a syncopal attack. Syncope results from a sudden impairment of brain metabolism usually due to a reduction in cerebral blood flow.