Final answer:
Atrial depolarization on an ECG is represented by the P wave, which occurs before the QRS complex, indicative of ventricular depolarization, and the T wave, which represents ventricular repolarization.
Step-by-step explanation:
Atrial depolarization on an electrocardiogram (ECG) is represented by the P wave. This small wave signifies the initiation of the electrical impulse that spreads through the atria and results in their contraction, which subsequently causes blood to be pumped into the ventricles. The P wave occurs before the larger QRS complex, which indicates ventricular depolarization, and the T wave, which signifies ventricular repolarization. It's important to note that atrial repolarization happens during the QRS complex and is masked by the stronger electrical activity of the ventricles.