**Core Concept:** Cardioselective beta-blockers are a class of medications that preferentially affect beta-1 receptors in the heart, while sparing beta-2 receptors in the lungs and bronchi. This results in less respiratory depression compared to non-selective beta-blockers.

**Why the Correct Answer is Right:** Atenolol is a cardioselective beta-blocker because it preferentially binds to beta-1 receptors in the heart, allowing for reduced respiratory depression compared to non-selective beta-blockers.

**Why Each Wrong Option is Incorrect:**
A. Propranolol is a non-selective beta-blocker, meaning it binds to both beta-1 and beta-2 receptors. This leads to significant respiratory depression due to blockade of beta-2 receptors in the lungs and bronchi.
B. ACE inhibitors are Angiotensin-converting enzyme inhibitors, which work through a different mechanism to lower blood pressure and not beta-blockers.
C. Calcium channel blockers are medications that act on voltage-gated calcium channels, and are unrelated to beta-blockers in terms of their mechanism of action.
D. Angiotensin II receptor blockers (ARBs) are medications that act on the angiotensin II receptors, not beta-blockers.

**Clinical Pearl / High-Yield Fact:** Understanding the selectivity of beta-blockers is crucial when treating patients with respiratory issues or those requiring reduced respiratory depression, such as those with asthma or chronic obstructive pulmonary disease (COPD). Cardioselective beta-blockers like atenolol are often preferred in these cases, while non-selective beta-blockers like propranolol should be used with caution due to increased risk of respiratory depression.

**Correct Answer:** Atenolol (Option A) is a cardioselective beta-blocker, while the other options are not beta-blockers at all.