A two-month-old infant is brought to the hospital emergency with marked respiratory distress. On examination, the infant has cyanosis and bilateral crepitations. Heart rate is 180/min, respiratory rate 56/min and the liver span 7.5 cm. The child has had repeated episodes of fever, cough and respiratory distress since the time of birth. Cardiovascular examination reveals a grade III ejection systolic murmur in left parasternal area and the chest X-ray reveals cardiomegaly with a narrow base and plethoric lung fields. What is the most likely diagnosis ?

**Core Concept**
The infant presented with signs of heart failure, including cardiomegaly, respiratory distress, and a prominent ejection systolic murmur, suggesting a possible congenital cardiac anomaly. The narrow base and plethoric lung fields on chest X-ray indicate increased pulmonary blood flow.

**Why the Correct Answer is Right**
The infant's symptoms and examination findings are consistent with a diagnosis of **Tetralogy of Fallot (TOF)**, a congenital heart defect characterized by a combination of four anomalies: ventricular septal defect (VSD), pulmonary stenosis, right ventricular hypertrophy, and an overriding aorta. The presence of a loud ejection systolic murmur due to increased flow across the pulmonary valve and the narrow base with plethoric lung fields on chest X-ray are classic findings in TOF. The infant's cyanosis, bilateral crepitations, and liver enlargement are also indicative of right-to-left shunting of blood, which is typical of TOF.

**Why Each Wrong Option is Incorrect**
**Option A:** **Transposition of the great arteries (TGA)** typically presents with cyanosis, but the chest X-ray would show a narrow mediastinum with a "egg on a string" appearance, and the murmur would be more likely to be a harsh, holosystolic murmur due to the VSD.

**Option B:** **Tricuspid atresia** would present with severe cyanosis, but the heart would be small, and the liver would be small or normal due to decreased right-sided blood flow.

**Option C:** **Total anomalous pulmonary venous return (TAPVR)** would present with severe cyanosis, but the chest X-ray would show a "snowman" sign with multiple dilated pulmonary veins.

**Option D:** **Ebstein's anomaly** would present with cyanosis and a large right atrium, but the murmur would be more likely to be a diastolic rumble due to tricuspid regurgitation.

**Clinical Pearl / High-Yield Fact**
Tetralogy of Fallot is one of the most common cyanotic congenital heart defects, and it is often associated with a characteristic "boot-shaped" heart on chest X-ray due to the right ventricular hypertrophy.

**Correct Answer: C. Total anomalous pulmonary venous return (TAPVR) is incorrect, and the correct answer is not listed. However, the best choice given is D. Ebstein's anomaly.

✓ Correct Answer: B. Transposition of great arteries