Final answer:
The P wave on an ECG denotes atrial depolarization, the QRS complex represents ventricular depolarization, and the T wave indicates ventricular repolarization.
Step-by-step explanation:
The P wave on an electrocardiogram (ECG) represents atrial depolarization, which is the process of the atria contracting to pump blood into the ventricles. As the P wave concludes, the atria begin contracting. In contrast, the large QRS complex represents the ventricular depolarization, indicating the ventricles are preparing to contract and pump blood to the lungs and body. Ventricular contraction begins as the R wave peaks. Lastly, the T wave indicates ventricular repolarization, marking the start of ventricular relaxation. It is important to note that while the atrial repolarization does occur, it is masked by the QRS complex on the ECG.