Final answer:
The QRS complex on an ECG represents ventricular depolarization, which is a critical phase preceding the contraction of the ventricles, enabling them to pump blood throughout the body.
Step-by-step explanation:
Ventricular depolarization is represented by the QRS complex on an electrocardiogram (ECG). It is during this phase that the ventricles of the heart undergo depolarization, which is necessary for them to contract and pump blood out to the lungs and body. The QRS complex requires a much stronger electrical signal than the atrial depolarization due to the larger size of the ventricular cardiac muscle. This phase is crucial as it precedes the ventricular contraction that effectively circulates blood.