Which of the following refers to the contraction of the ventricles following depolarization?

• A. P wave
• B. T wave
• C. QRS complex
• D. U wave

Answer: (C)

Ventricular contraction is triggered by the electrical depolarization of the ventricles, and this event is captured on the ECG as the QRS complex. The rapid, sharp deflections of the QRS reflect the ventricles depolarizing as the impulse travels through the His-Purkinje system and ventricular muscle, leading to systole. The P wave, by contrast, is atrial depolarization and does not depict ventricular activity. The T wave shows ventricular repolarization, which occurs as the ventricles recover and relax, not during contraction. The U wave, when present, is an additional repolarization feature and is not the main driver of ventricular contraction. So, the contraction following depolarization is represented by the QRS complex.