**Core Concept**
The patient's symptoms and physical examination findings suggest a congenital heart defect involving the pulmonary valve or the right ventricle. The wide, fixed split S2 is a classic sign of increased flow across the pulmonary valve, and the ejection systolic murmur is consistent with increased flow or turbulence.

**Why the Correct Answer is Right**
The patient's presentation is most likely due to a ventricular septal defect (VSD) with pulmonary hypertension, leading to right ventricular hypertrophy and increased flow across the pulmonary valve. The left axis deviation on ECG is consistent with right ventricular hypertrophy. The increased flow across the pulmonary valve causes the wide, fixed split S2.

**Why Each Wrong Option is Incorrect**
* **Option A:** While aortic stenosis can cause ejection systolic murmur and increased flow across the aortic valve, it typically presents with a harsh, crescendo-decrescendo murmur in the right second intercostal space, not a wide, fixed split S2.
* **Option B:** Tetralogy of Fallot typically presents with a cyanotic congenital heart disease with a harsh, pansystolic murmur due to pulmonary stenosis, and a single S2 due to right ventricular outflow tract obstruction.
* **Option C:** Mitral regurgitation typically presents with a pansystolic murmur in the apex, not an ejection systolic murmur in the left second intercostal space.

**Clinical Pearl / High-Yield Fact**
A wide, fixed split S2 is a classic sign of increased flow across the pulmonary valve, which can be seen in conditions such as VSD with pulmonary hypertension, atrial septal defect, or pulmonary regurgitation.

**Correct Answer:** C.