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

**Core Concept**
The clinical presentation of central cyanosis, clubbing, and a systolic thrill in a young child suggests a congenital heart defect with increased pulmonary blood flow and right-to-left shunting. This presentation is classic for a patent ductus arteriosus (PDA) with pulmonary hypertension.

**Why the Correct Answer is Right**
The presence of a systolic thrill over the left middle sternal border and a parasternal heave indicates an increased flow across the pulmonary valve, which is typical for PDA. The absence of a diastolic murmur and only the aortic component of the second heart sound being audible suggests pulmonary hypertension. This is a result of the increased flow and resistance in the pulmonary vasculature.

**Why Each Wrong Option is Incorrect**
* **Option A:** Tetralogy of Fallot (TOF) typically presents with cyanosis, clubbing, and a harsh systolic ejection murmur, but the absence of a diastolic murmur and the presence of a parasternal heave make this less likely. TOF also typically presents with a smaller heart size.
* **Option B:** Ventricular septal defect (VSD) can present with increased pulmonary blood flow and cyanosis, but the absence of a diastolic murmur and the presence of a parasternal heave suggest pulmonary hypertension, which is not typical for VSD.
* **Option C:** Atrial septal defect (ASD) typically presents with increased pulmonary blood flow, but the absence of a diastolic murmur and the presence of a parasternal heave suggest pulmonary hypertension, which is not typical for ASD.

**Clinical Pearl / High-Yield Fact**
In children with suspected congenital heart disease, the presence of a systolic thrill and a parasternal heave should raise suspicion for increased pulmonary blood flow and right-to-left shunting.

**Correct Answer:** C.

✓ Correct Answer: D. Tetralogy of Fallot