A two-year old boy presented with episodes of becoming dusky. On examination, there was central cyanosis and clubbing. There was no pallor, oedema or respiratory distress. The hea was normal sized with a parasternal heave. A systolic thrill was palpable over the left middle sternal border. First hea sound was normal and only the aoic component was audible in the second hea sound. Liver was not enlarged – What would be the likely diagnosis ?

**Core Concept**
The clinical presentation of central cyanosis, clubbing, and a systolic thrill over the left middle sternal border in a young child suggests a congenital heart defect with an abnormal blood flow pattern.

**Why the Correct Answer is Right**
The presence of a systolic thrill and a parasternal heave, along with a normal first heart sound and an accentuated aortic component of the second heart sound, is characteristic of a condition known as Tetralogy of Fallot (TOF). This congenital heart defect is caused by a combination of four anatomical abnormalities: ventricular septal defect (VSD), pulmonary stenosis, right ventricular hypertrophy, and an overriding aorta. The VSD allows blood to flow from the left ventricle to the right ventricle, while the pulmonary stenosis restricts blood flow to the lungs, resulting in cyanosis. The right ventricular hypertrophy is a compensatory response to the increased resistance in the pulmonary circulation.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is not provided.
* **Option B:** This option is not provided.
* **Option C:** This option is not provided.
* **Option D:** This option is not provided.

**Clinical Pearl / High-Yield Fact**
The "tet" sign, which refers to the presence of a systolic thrill over the left middle sternal border, is a classic clinical finding in Tetralogy of Fallot. This sign is due to the abnormal blood flow through the VSD and the pulmonary stenosis.

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

✓ Correct Answer: D. Tetralogy of Fallot