**Core Concept**
Tetralogy of Fallot (TOF) is a congenital heart defect characterized by a combination of four anatomical abnormalities: ventricular septal defect (VSD), pulmonary stenosis, right ventricular hypertrophy, and an overriding aorta. This results in cyanosis due to decreased pulmonary blood flow and increased systemic vascular resistance.

**Why the Correct Answer is Right**
The correct answer is Tetralogy of Fallot because it is the most common cyanotic heart disease, accounting for approximately 5-10% of all congenital heart defects. The pathophysiology involves a VSD that allows blood to flow from the left to the right ventricle, resulting in a "right-to-left" shunt. This shunt bypasses the lungs, leading to deoxygenated blood being pumped directly into the systemic circulation, causing cyanosis.

**Why Each Wrong Option is Incorrect**
* **Option A (Hypoplastic Left Heart Syndrome)**: This is a cyanotic heart defect, but it is not the most common type.
* **Option B (Tricuspid Atresia)**: This is a cyanotic heart defect, but it is less common than Tetralogy of Fallot.
* **Option C (Eisenmenger's Syndrome)**: This is a complication of uncorrected congenital heart defects, but it is not a specific type of cyanotic heart disease.

**Clinical Pearl / High-Yield Fact**
Tetralogy of Fallot is often associated with a "boot-shaped" heart on chest radiography due to right ventricular hypertrophy.

**Correct Answer:** C. Tetralogy of Fallot.