**Core Concept**
The human heart's electrical activity is governed by the action potential, a complex process involving the coordinated contraction and relaxation of cardiac myocytes. Repolarization is the final phase of the action potential, where the membrane potential returns to its resting state, allowing the heart to reset for the next contraction.

**Why the Correct Answer is Right**
During repolarization, the electrical activity in the heart proceeds from the epicardium to the endocardium. The apical endocardium is the last part of the heart to be repolarized due to the unique electrophysiological properties of cardiac myocytes. The endocardial layer, being closer to the Purkinje fibers, receives the action potential later than the epicardial layer, resulting in delayed repolarization. This delayed repolarization is essential for the proper functioning of the heart, ensuring a coordinated contraction and relaxation of cardiac myocytes.

**Why Each Wrong Option is Incorrect**
**Option A:** The apical epicardium is actually one of the first areas to be repolarized, not the last. This is because the epicardial layer receives the action potential earlier than the endocardial layer.

**Option C:** The epicardium of the base of the left ventricle (LV) is not the last part of the heart to be repolarized. The electrophysiological properties of the cardiac myocytes in this region do not contribute to delayed repolarization.

**Option D:** The endocardium of the base of the LV is also not the last part of the heart to be repolarized. As mentioned earlier, the apical endocardium is the last part of the heart to be repolarized due to its unique electrophysiological properties.

**Clinical Pearl / High-Yield Fact**
The unique electrophysiological properties of cardiac myocytes, particularly in the apical endocardium, are essential for the proper functioning of the heart. Understanding these properties is crucial for diagnosing and managing cardiac arrhythmias.

**✓ Correct Answer: B. Apical endocardium**