**Core Concept**
Eclampsia is a severe complication of preeclampsia characterized by seizures in a pregnant woman, often associated with cardiovascular and electrolyte disturbances. In this scenario, palpitations in a stable patient suggest arrhythmia, which may be related to eclampsia-induced electrolyte imbalance.

**Why the Correct Answer is Right**
Palpitations in a patient with eclampsia may be due to hyperkalemia, a common electrolyte disturbance in this condition. The patient's stable vitals suggest that the arrhythmia is not life-threatening at this moment. The next best step would be to correct the underlying electrolyte imbalance. Magnesium sulfate, the first-line treatment for eclampsia, also has a role in treating arrhythmias caused by hyperkalemia.

**Why Each Wrong Option is Incorrect**
**Option A:** Administering digoxin would not be the best choice in this scenario, as digoxin can exacerbate hyperkalemia and is not indicated for treating arrhythmias in the context of eclampsia.

**Option B:** Starting a beta-blocker would not address the underlying electrolyte imbalance causing the palpitations. Beta-blockers may also worsen bradycardia or heart block in a patient with eclampsia.

**Option C:** Performing an immediate cesarean section would not directly address the palpitations or the underlying electrolyte imbalance. While cesarean delivery is often necessary in eclampsia, it is not the next best step in this scenario.

**Option D:** Administering a calcium channel blocker would not be the best choice, as calcium channel blockers can worsen hyperkalemia and are not indicated for treating arrhythmias in the context of eclampsia.

**Clinical Pearl / High-Yield Fact**
In patients with eclampsia, palpitations are often caused by hyperkalemia, and correcting the electrolyte imbalance with magnesium sulfate is crucial. Remember the "rule of sixes" for magnesium sulfate: 4-6 grams IV over 5-10 minutes, with continuous ECG monitoring.

**Correct Answer:** C.