Final answer:
The P wave of a normal electrocardiogram represents atrial depolarization. It precedes atrial contraction and is followed by the QRS complex, representing ventricular depolarization, with ventricular repolarization denoted by the T wave.
Step-by-step explanation:
The P wave of a normal electrocardiogram indicates atrial depolarization. This small wave represents the depolarization of the atria and is followed by atrial contraction (systole) approximately 25 ms after its onset.
The QRS complex, which follows the P wave, denotes the ventricular depolarization and the subsequent ventricular contraction. The T wave signifies ventricular repolarization, indicating the beginning of ventricular relaxation. It is also important to note that atrial repolarization occurs during the QRS complex but is masked by the much stronger electrical activity associated with ventricular depolarization.