A person with second degree heart block has a delay in the electrical impulse that travels through the heart. This delay results in incomplete heartbeats.

An electrical impulse stimulates the muscle fibers in the heart to contract. The impulse spreads through the heart in a very organized manner, so that the atria contract first, followed by the ventricles. In second degree heart block, the electrical impulse stimulates the ventricles to beat most of the time, but some electrical impulses do not stimulate the ventricle to beat.