The electrical signal from the SA node must pass through the AV node and continue on through the conduction pathways in the ventricles. If the AV node is impaired, the impulse may become slowed, irregular, or stopped. This condition is called heart block because the electrical impulse is blocked from proceeding normally from the atria to the ventricles.
Heart block is described as first, second, or third degree.
How slow the ventricular rate becomes depends on the degree of heart block. A pacemaker can correct the effects of this condition. More about Impaired electrical system . The four sections of the heart through which blood is pumped. The two upper chambers are called the left atrium and right atrium.