**Core Concept**
Metoprolol and captopril are two medications with different primary mechanisms of action. Metoprolol is a beta-1 selective adrenergic receptor blocker, primarily used to reduce heart rate and blood pressure. Captopril, on the other hand, is an angiotensin-converting enzyme (ACE) inhibitor, used to lower blood pressure by inhibiting the conversion of angiotensin I to angiotensin II.

**Why the Correct Answer is Right**
The negative inotropic effect refers to a decrease in the contractility of the heart muscle. Metoprolol, by blocking beta-1 adrenergic receptors, decreases the heart's response to catecholamines, leading to a decrease in contractility. This results in a decrease in the heart's ability to pump blood efficiently. Captopril, however, does not directly affect the heart's contractility but rather affects the renin-angiotensin-aldosterone system, leading to vasodilation and decreased peripheral resistance.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it is not specific to metoprolol and captopril. Both medications have different primary mechanisms of action.
**Option B:** This option is incorrect because it is not a characteristic of captopril. Captopril primarily affects blood pressure through vasodilation and decreased peripheral resistance.
**Option C:** This option is incorrect because it is not a characteristic of metoprolol. Metoprolol primarily affects the heart rate and contractility through beta-1 adrenergic receptor blockade.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that beta-blockers like metoprolol can cause a negative inotropic effect, which can be problematic in patients with heart failure or those who are hypotensive.

**Correct Answer: A. Metoprolol.**