Loud, harsh murmur heard along the left sternal border is most characteristic of which defect?

• A. Atrial septal defect
• B. Patent ductus arteriosus
• C. Tetralogy of Fallot
• D. Ventricular septal defect

Answer: (D)

A holosystolic, harsh murmur heard best at the left lower sternal border points to a ventricular septal defect. The murmur comes from turbulent blood flowing from the left ventricle to the right ventricle throughout systole, so it lasts the entire S1–S2 interval (pansystolic) and sounds rough or harsh. The intensity often reflects defect size: small defects have loud, high-velocity murmurs, while large defects may have softer murmurs because the pressure difference is smaller.

In contrast, an atrial septal defect usually shows a systolic ejection murmur at the left upper sternal border from increased flow across the pulmonary valve and a fixed split S2. Patent ductus arteriosus yields a continuous machine-like murmur best heard near the left infraclavicular area. Tetralogy of Fallot can have a harsh systolic murmur due to right ventricular outflow tract obstruction, but it is typically best heard at the left upper sternal border and is associated with cyanosis and a different overall clinical picture.