Next, the electrical impulse travels through the atrioventricular (AV) node to reach the muscle cells of the ventricles, causing them to depolarize (change their electrical charge). Because the walls of the ventricles are much larger than those of the atria, the amount of electrical change is greater, and the pen draws a larger wave. When the electrical change finishes, the pen returns to the neutral position, leaving a mark called the QRS complex, which usually consists of a Q wave, an R wave, and an S wave. The electrical changes occurring as the ventricular muscle fibers repolarize (recover their electrical
charge) produces a T wave as the pen moves again, ending the pattern created by a single cardiac cycle. The ECG peaks and valleys thus indicate whether the electrical impulses are traveling through the heart at the right speed in the right order.