Atrioventricular node: The electrical relay station between the upper and lower chambers of the heart. Abbreviated AV node. Electrical signals from the atria must pass through the AV node to reach the ventricles. The AV node, which controls the heart rate, is one of the major elements in the cardiac conduction system. The AV node serves as an electrical relay station, slowing the electrical current sent by the sinoatrial (SA) node before the signal is permitted to pass down through to the ventricles. This delay ensures that the atria have an opportunity to fully contract before the ventricles are stimulated. After passing the AV node, the electrical current travels to the ventricles, along special fibers embedded in the walls of the lower part of the heart.