## **Core Concept**
Cardioselective beta blockers are drugs that primarily block β1-adrenergic receptors in the heart, reducing heart rate and myocardial contractility with less effect on airway resistance and peripheral circulation. This selectivity is beneficial in patients with asthma or chronic obstructive pulmonary disease (COPD). The main β1 receptors are located in the heart.

## **Why the Correct Answer is Right**
Propranolol is a non-selective beta blocker, meaning it blocks both β1 and β2 receptors. This characteristic makes it non-cardioselective. In contrast, drugs like metoprolol, bisoprolol, and atenolol are examples of cardioselective beta blockers.

## **Why Each Wrong Option is Incorrect**
* **Option A:** Metoprolol is a cardioselective beta blocker, primarily affecting β1 receptors in the heart.
* **Option B:** Bisoprolol is also cardioselective, with a high affinity for β1 receptors.
* **Option C:** Atenolol is another cardioselective beta blocker.

## **Clinical Pearl / High-Yield Fact**
A key clinical point to remember is that while cardioselective beta blockers are safer in patients with respiratory diseases, this selectivity can be lost at high doses. Therefore, even cardioselective beta blockers should be used with caution in patients with asthma or COPD.

## **Correct Answer:** D. Propranolol.