Which of the following is an example of a selective beta-1 blocker?

Metoprolol is an example of a selective beta-1 blocker because it specifically targets beta-1 adrenergic receptors, which are primarily located in the heart. By selectively blocking these receptors, metoprolol reduces heart rate and decreases myocardial contractility, leading to a decrease in cardiac output and ultimately lowering blood pressure. This selectivity makes it effective for treating conditions like hypertension and heart failure, as it minimizes the potential side effects that could arise from blocking beta-2 receptors, which are involved in bronchodilation and other functions beyond the heart.

In contrast, other options listed do not exhibit the same selectivity. Atenolol, while also a selective beta-1 blocker like metoprolol, is not the only choice available and is usually considered alongside metoprolol in clinical discussions. Carvedilol and propranolol are non-selective beta blockers; they block both beta-1 and beta-2 receptors, which can lead to additional effects such as bronchoconstriction and peripheral vasoconstriction. Thus, metoprolol's selective action allows for targeted therapeutic effects with fewer unwanted side effects related to the beta-2 receptor inhibition.