**Question:** Repolarization is due to

A. the T-wave
B. the U-wave
C. the early repolarization phase
D. the plateau phase

**Core Concept:** Repolarization is a part of the cardiac action potential, which is essential for the heart's electrical conduction system to function properly. It involves the restoration of the membrane potential back to its resting state, ensuring the heart muscle contracts and relaxes in a coordinated manner.

**Why the Correct Answer is Right:** Repolarization is primarily due to the T-wave, which is a phase of the action potential. The T-wave represents the return of the membrane potential to its resting state, ensuring proper heart muscle contraction and relaxation.

**Why Each Wrong Option is Incorrect:**

A. The T-wave (correct answer) is responsible for repolarization, not the U-wave. The U-wave is a small, inverted waveform that follows the T-wave and represents the end of the action potential.

B. The U-wave is mentioned as an incorrect answer because it only represents the end of the action potential, while repolarization is a separate phase of the action potential.

C. Early repolarization phase is not the correct answer because it refers to a specific phase (phase 2) within the action potential, rather than the overall repolarization process.

D. The plateau phase is part of the action potential, but it is not responsible for repolarization. Repolarization occurs during the T-wave and is essential for the heart's normal function.

**Clinical Pearl:** Understanding the phases of the cardiac action potential is crucial for recognizing abnormal cardiac rhythms and diagnosing cardiac disorders, such as long QT syndrome. Correct interpretation of the ECG tracing helps in making accurate clinical decisions and appropriate treatment plans for patients.