Atrioventricular block is a condition where the electrical signals between the heart's upper chambers (atria) and lower chambers (ventricles) are delayed or blocked. This disruption can affect the heart's ability to pump blood effectively, leading to symptoms like fatigue, dizziness, or fainting. There are three degrees of atrioventricular block. In first-degree block, signals are delayed but still reach the ventricles. In second-degree block, some signals are blocked, causing missed heartbeats. In third-degree block, no signals reach the ventricles, which can be life-threatening and often requires medical intervention, such as a pacemaker.