Third-degree block, also known as complete heart block, is a condition where the electrical signals between the heart's upper chambers (atria) and lower chambers (ventricles) are completely interrupted. This means that the atria can beat independently of the ventricles, leading to a disconnection in the heart's rhythm. As a result, the heart may not pump blood effectively, which can cause symptoms like fatigue, dizziness, or fainting. This condition can be caused by various factors, including damage to the heart tissue from a heart attack, inflammation, or certain medications. Treatment often involves the implantation of a pacemaker, a device that helps regulate the heart's rhythm by sending electrical signals to the ventricles.