**Core Concept**
The earliest reliable enzyme to increase in Acute Myocardial Infarction (AMI) is related to the **biochemical markers** of cardiac damage. In AMI, various enzymes are released into the bloodstream due to the necrosis of cardiac muscle cells.

**Why the Correct Answer is Right**
The correct answer is related to the enzyme that is first released into the bloodstream after cardiac cell death. This enzyme is **Troponin**, specifically **Troponin T** or **Troponin I**, but another enzyme is even earlier, which is **Myoglobin** and then the **CK-MB** fraction of **Creatine Kinase**. However, **Troponin** is more specific and sensitive.

**Why Each Wrong Option is Incorrect**
**Option A:** May be incorrect if it is not the earliest marker.
**Option B:** May be incorrect if it is not the earliest marker.
**Option C:** May be incorrect if it is not the earliest marker.
**Option D:** May be incorrect if it is not the earliest marker.

**Clinical Pearl / High-Yield Fact**
In clinical practice, **Troponin** levels are used to diagnose AMI, but **Myoglobin** is not as specific. The earliest increase is seen in **Myoglobin**, but **Troponin** is more reliable due to its specificity.

**Correct Answer:** D. Troponin