**Core Concept**
Angina pectoris is a condition characterized by transient myocardial ischemia, typically resulting from reduced blood flow to the heart muscle, leading to chest pain and other symptoms. This condition is often associated with atherosclerotic coronary artery disease.

**Why the Correct Answer is Right**
Angina pectoris can indeed result in a medical emergency in the dental office due to its potential to trigger a myocardial infarction (MI). The physical stress of dental procedures, combined with the patient's underlying coronary artery disease, can precipitate an MI. The symptoms described, such as substernal pain, facial pallor, and cold perspiration, are classic signs of angina pectoris. The pathophysiology involves reduced blood flow to the heart muscle, leading to ischemia and pain.

**Why Each Wrong Option is Incorrect**
**Option A:** Aortic dissection is a serious condition involving a tear in the aortic wall, but it typically presents with severe, tearing chest pain radiating to the back, rather than substernal pain.
**Option B:** Pulmonary embolism is a condition involving a blockage of the pulmonary arteries, often presenting with sudden onset dyspnea and tachypnea, rather than substernal pain and cold perspiration.
**Option C:** Gastroesophageal reflux disease (GERD) is a condition involving acid reflux into the esophagus, typically presenting with heartburn and regurgitation, rather than substernal pain and systemic symptoms.

**Clinical Pearl / High-Yield Fact**
In patients with a history of coronary artery disease, dental procedures can precipitate a myocardial infarction. It is essential to identify and manage these patients appropriately in the dental office.

**Correct Answer:** C. Angina pectoris.