**Core Concept**
Sarcoidosis is a systemic granulomatous disease that can affect multiple organs, including the lungs, heart, and nervous system. Cardiac involvement, particularly cardiac arrhythmias, is a significant concern in sarcoidosis patients.

**Why the Correct Answer is Right**
The most common cause of sudden death in sarcoidosis is cardiac arrhythmia, specifically ventricular fibrillation. This occurs due to the inflammation and scarring of cardiac tissue, leading to conduction abnormalities and increased risk of life-threatening arrhythmias. The granulomatous inflammation in the cardiac tissue can disrupt the normal functioning of the cardiac conduction system, resulting in arrhythmias that can be fatal.

**Why Each Wrong Option is Incorrect**
**Option A:** Cardiac failure is a potential complication of sarcoidosis, but it is not the most common cause of sudden death.
**Option B:** Hypercalcemia can occur in sarcoidosis due to increased 1,25-dihydroxyvitamin D production, but it is not directly related to sudden death.
**Option C:** Pulmonary involvement is common in sarcoidosis, but it is not typically associated with sudden death.

**Clinical Pearl / High-Yield Fact**
Sarcoidosis patients with cardiac involvement should be closely monitored for cardiac arrhythmias, and electrocardiogram (ECG) monitoring may be necessary in high-risk patients.

**Correct Answer: C. Pulmonary involvement is common in sarcoidosis, but it is not typically associated with sudden death.