**Core Concept**
LDH (Lactate Dehydrogenase) isoenzymes are a group of five enzymes that play a crucial role in the anaerobic glycolysis pathway, catalyzing the conversion of lactate to pyruvate. LDH isoenzymes are tissue-specific, meaning they are predominantly found in different organs and tissues, allowing for the identification of tissue damage through the measurement of specific isoenzyme levels in the blood.

**Why the Correct Answer is Right**
LDH-2 isoenzyme is predominantly found in the heart and is released into the bloodstream when cardiac tissue is damaged. This is because LDH-2 isoenzyme is specifically localized in the cytoplasm of cardiac muscle cells. When cardiac muscle cells are injured or die, they release LDH-2 isoenzyme into the bloodstream, where it can be measured to diagnose and monitor cardiac damage.

**Why Each Wrong Option is Incorrect**
**Option A:** LDH-1 isoenzyme is predominantly found in the liver and not the heart.
**Option B:** LDH-4 isoenzyme is predominantly found in the lungs and not the heart.
**Option C:** LDH-5 isoenzyme is predominantly found in skeletal muscle and not the heart.

**Clinical Pearl / High-Yield Fact**
The ratio of LDH-1 to LDH-2 isoenzyme levels can be used to differentiate between myocardial infarction and liver damage. In myocardial infarction, the LDH-2 level is elevated, whereas in liver damage, the LDH-1 level is elevated.

**Correct Answer: D. LDH-2.**