**Core Concept**
Digitalis-induced ventricular arrhythmia occurs due to an excessive increase in intracellular calcium levels, leading to abnormal cardiac excitability. This is often caused by an overdose of cardiac glycosides, such as digoxin.

**Why the Correct Answer is Right**
The drug of choice in digitalis-induced ventricular arrhythmia is a beta-blocker, specifically **propranolol**. Propranolol works by blocking beta-1 receptors in the heart, reducing the sympathetic tone, and thus decreasing the intracellular calcium levels. This, in turn, helps to stabilize the cardiac membrane and prevent arrhythmias.

**Why Each Wrong Option is Incorrect**
* **Option A:** Magnesium sulfate is used to treat digitalis toxicity, but it's not the first-line treatment for ventricular arrhythmias. Magnesium can help stabilize the cardiac membrane, but it's more effective in treating atrial arrhythmias.
* **Option B:** Phenytoin is an antiarrhythmic medication, but it's not the preferred choice for digitalis-induced ventricular arrhythmia. Phenytoin can worsen arrhythmias in some cases.
* **Option D:** Amiodarone is a broad-spectrum antiarrhythmic agent, but it's not the first-line treatment for digitalis-induced ventricular arrhythmia. Amiodarone has a narrow therapeutic index and can cause more harm than benefit in this scenario.

**Clinical Pearl / High-Yield Fact**
In cases of digitalis toxicity, always remember to administer **magnesium sulfate** (1-2 grams IV over 1-2 minutes) to stabilize the cardiac membrane and prevent further arrhythmias. This can be followed by **digoxin-specific antibody fragments (Fab)** if the patient's condition worsens.

**Correct Answer:** C. Propranolol