Final answer:
The P-wave of an ECG represents atrial depolarization and contraction, the QRS complex illustrates ventricular depolarization, and the T wave indicates ventricular repolarization and relaxation.
Step-by-step explanation:
An ECG is a recording of the electrical activity of the heart. During the P-wave, the atria depolarize, which initiates the atrial contraction following shortly after the start of the P-wave. The QRS complex indicates the depolarization of ventricles, representing a much stronger electrical signal due to the ventricles' larger muscle mass, with ventricular contraction starting at the peak of the R wave. Finally, the T wave signifies the repolarization of the ventricles, marking the start of their relaxation phase.
The detailed steps of each waveform on the ECG represent critical phases in the heart's electrical cycle, aligning with the mechanical actions of the heart muscle. As such, the P-wave is associated with atrial depolarization and contraction into the ventricles. The large QRS complex follows, related to the ventricles receiving a more potent electrical signal, preceding their contraction. The T wave concludes the cycle by indicating the repolarization of the ventricles as they move into the relaxation phase, ready for the next heartbeat.