**Core Concept**
Long-term secondary prevention following myocardial infarction involves the use of medications to reduce the risk of recurrent cardiovascular events, primarily by inhibiting platelet aggregation and lowering blood pressure. This is achieved through the inhibition of the renin-angiotensin-aldosterone system (RAAS) and the blockade of the platelet activation pathway.

**Why the Correct Answer is Right**
Beta-blockers, such as Metoprolol, are recommended for long-term secondary prevention following myocardial infarction due to their ability to reduce heart rate, contractility, and blood pressure. They work by blocking the effects of epinephrine and norepinephrine on the beta-1 receptors in the heart, thereby decreasing the heart rate and the force of contraction. This leads to a reduction in myocardial oxygen demand, which is particularly beneficial in the setting of a previous myocardial infarction.

**Why Each Wrong Option is Incorrect**
**Option A:** Aspirin is indeed used in the management of myocardial infarction, but it is not the primary drug for long-term secondary prevention. Aspirin works by inhibiting platelet aggregation through the blockade of cyclooxygenase (COX) enzymes, but its benefits are more pronounced in the acute setting.
**Option B:** Thiazide diuretics, such as Hydrochlorothiazide, are used to manage hypertension and heart failure but are not the primary drugs for long-term secondary prevention following myocardial infarction.
**Option C:** ACE inhibitors, such as Lisinopril, are used to manage hypertension and heart failure but are not the primary drugs for long-term secondary prevention following myocardial infarction.

**Clinical Pearl / High-Yield Fact**
Beta-blockers are a crucial component of long-term secondary prevention following myocardial infarction, and their benefits are most pronounced when started within the first 24-48 hours after the event.

**Correct Answer: C. Metoprolol**