As discussed in Chapter 2, the QRS complex represents the unopposed electrical forces associated with ventricular depolarization. Normally, the interventricular septum is the first part of the ventricles to be depolarized. Its depolarization, from the left ventricular side to the right, is responsible for the initial part of the QRS complex and is the cause of the narrow Q wave (usually no more than 0.02 seconds) seen in some leads on the normal electrocardiogram. The two ventricles then depolarize more or less simultaneously. from apex to base. It is the unopposed or uncancelled electrical forces representing the larger mass of the left ventricle that is responsible for the remainder of the QRS complex.