A young female presents with history of dyspnoea on exeion. On examination, she has wide, fixed split S2 with ejection systolic murmur (IIINI) in left second intercostal space. Her ECG shows left axis detion. The most probable diagnosis is ?

**Core Concept**
The patient's clinical presentation is suggestive of a congenital heart defect characterized by an abnormal opening between the atria, leading to abnormal blood flow and resulting in characteristic physical examination findings and electrocardiographic changes.

**Why the Correct Answer is Right**
The diagnosis is most likely atrial septal defect (ASD). The wide, fixed split S2 is due to the increased flow across the pulmonary valve, causing a delay in the closure of the pulmonary valve. The ejection systolic murmur in the left second intercostal space is due to increased flow across the pulmonary valve. The left axis deviation on ECG is also consistent with ASD, as it is a common electrocardiographic finding in patients with this condition. The increased flow through the pulmonary valve also leads to pulmonary hypertension, which can cause right ventricular hypertrophy and eventual left axis deviation.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is not provided, so there's no explanation for it.
**Option B:** This option is also not provided, so there's no explanation for it.
**Option C:** This option is also not provided, so there's no explanation for it.
**Option D:** This option is also not provided, so there's no explanation for it.

**Clinical Pearl / High-Yield Fact**
A key point to remember is that a wide, fixed split S2 is a classic finding in ASD, and it is often associated with a harsh ejection systolic murmur in the left second intercostal space.

**Correct Answer:** .

✓ Correct Answer: C. Ostium primum atrial septal defect.