## **Core Concept**
The antianginal effect of propranolol, a non-selective beta-blocker, is primarily related to its ability to decrease myocardial oxygen demand. This is achieved through its effects on heart rate, contractility, and blood pressure. By reducing these factors, propranolol helps in managing angina pectoris.

## **Why the Correct Answer is Right**
The correct answer, **D. Decrease in heart rate and contractility**, is right because propranolol's antianginal effect is mainly attributed to its negative chronotropic (decrease in heart rate) and negative inotropic (decrease in contractility) effects. By blocking beta-1 receptors in the heart, propranolol decreases the heart rate and the force of contraction, which in turn reduces the myocardial oxygen demand. This reduction in oxygen demand helps in alleviating the symptoms of angina.

## **Why Each Wrong Option is Incorrect**
- **Option A:** Increase in heart rate and contractility - This is the opposite of what propranolol does. Increasing heart rate and contractility would increase myocardial oxygen demand, worsening angina.
- **Option B:** Increase in preload - Propranolol does not significantly increase preload as a mechanism for its antianginal effect. In fact, by reducing heart rate, it can allow for better diastolic filling, but this is not its primary mechanism.
- **Option C:** Vasodilation - While some antianginal drugs work by causing vasodilation (e.g., nitrates), propranolol's primary antianginal effect is not through vasodilation but through reduction of heart rate and contractility.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is that beta-blockers like propranolol are a cornerstone in the management of angina pectoris, especially in patients without contraindications such as significant bradycardia, heart block, or severe heart failure. They are often used in combination with other antianginal agents.

## **Correct Answer:** D. Decrease in heart rate and contractility