## **Core Concept**
The question tests the understanding of anti-anginal drugs and their use in both prophylaxis and treatment of angina. Angina pectoris is a condition characterized by chest pain due to transient myocardial ischemia. The management involves drugs that either reduce myocardial oxygen demand or increase oxygen supply.

## **Why the Correct Answer is Right**
The correct answer, **Propranolol**, is a beta-blocker. Beta-blockers decrease the heart rate and contractility, thereby reducing myocardial oxygen demand. They are effective in both the prophylaxis and treatment of angina because they can prevent the occurrence of angina by reducing the frequency of episodes and alleviate symptoms during an episode by decreasing the workload on the heart.

## **Why Each Wrong Option is Incorrect**
- **Option A:** Nifedipine is a calcium channel blocker that primarily causes vasodilation, reducing blood pressure and afterload, which in turn decreases myocardial oxygen demand. While it can be used for angina treatment, it's not the first choice for prophylaxis in the same way beta-blockers are.
- **Option B:** Nitroglycerin is used for the immediate relief of angina symptoms. It works by causing vasodilation, which decreases preload and subsequently reduces myocardial oxygen demand. However, its use in prophylaxis is limited due to the development of tolerance and its short duration of action.
- **Option D:** Diltiazem is also a calcium channel blocker with effects on both cardiac conduction and vascular smooth muscle. It can be used for angina but is not as commonly associated with both prophylaxis and treatment as beta-blockers.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is that beta-blockers like **Propranolol** are recommended for patients with angina without contraindications (e.g., certain types of heart block, severe asthma) because they reduce mortality and morbidity in patients with coronary artery disease, in addition to controlling symptoms.

## **Correct Answer: C. Propranolol**