Which congenital defect is classically associated with fixed splitting of the second heart sound and a systolic ejection murmur best heard at the left second intercostal space?

• A. Harsh holosystolic murmur at LSB
• B. Continuous machinery murmur
• C. Dull murmur at apex
• D. Fixed splitting of S2 and systolic ejection murmur at 2nd left ICS

Answer: (D)

This question hinges on recognizing a classic presentation of an atrial septal defect. The fixed splitting of the second heart sound along with a systolic ejection murmur best heard at the left second intercostal space comes from increased blood flow through the pulmonic valve due to a left-to-right shunt at the atrial level. The extra flow prolongs right ventricular systole and delays pulmonic valve closure, but this delay remains constant regardless of breathing, creating a fixed S2 split. The murmur is from the higher velocity flow across the pulmonic valve, producing a systolic ejection murmur at the pulmonic area.

In contrast, a harsh holosystolic murmur at the left sternal border suggests a ventricular septal defect, a continuous machinery murmur points to a patent ductus arteriosus, and a dull murmur at the apex could reflect mitral valve or flow murmurs—none of which produce the fixed S2 splitting paired with the pulmonic-area murmur seen in ASD.