**Core Concept**
The question is testing the student's knowledge of medication management in patients with cardiovascular diseases. The correct answer is related to the management of atrial fibrillation, a common cardiac arrhythmia.

**Why the Correct Answer is Right**
The correct answer is **Digoxin**. Digoxin is a cardiac glycoside that is used to control ventricular rate in patients with atrial fibrillation. It works by inhibiting the sodium-potassium ATPase pump, leading to an increase in intracellular calcium and a subsequent increase in contractility. This effect is beneficial in patients with atrial fibrillation, as it helps to reduce the ventricular rate and improve symptoms.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is not relevant to the management of atrial fibrillation.
**Option B:** This option is not a medication used for atrial fibrillation.
**Option C:** This option is not a medication used for atrial fibrillation; it is actually a medication used for hypertension.

**Clinical Pearl / High-Yield Fact**
In patients with atrial fibrillation, digoxin is often used in conjunction with beta-blockers to control the ventricular rate. It is essential to monitor serum digoxin levels closely in these patients to avoid toxicity.

**Correct Answer: C. **