What is the T wave in an ECG?

• A. Depolarization of the atria.
• B. Repolarization of the ventricles.
• C. Ventricular contraction.
• D. No electrical activity.

Answer: (B)

The T wave shows ventricular repolarization—the ventricles returning to their resting electrical state after they have contracted. In the ECG sequence, atrial depolarization creates the P wave, ventricular depolarization creates the QRS complex and triggers ventricular contraction, and the T wave comes after as the ventricular muscle cells reset. If there were no electrical activity, you’d see no waves at all. So the T wave specifically marks the ventricles returning to baseline.