Ventricular septal defect murmurs may not be present at birth but become audible later as what develops?

• A. Pulmonary hypertension
• B. Coarctation
• C. Patent ductus arteriosus
• D. Anemia

Answer: (A)

VSD murmurs depend on the pressure difference and flow across the defect, which is shaped by the state of the pulmonary circulation after birth. In a newborn with a large VSD, the pulmonary vasculature initially has high resistance, so the left-to-right shunt is relatively small and turbulent flow across the septum may be minimal, making the murmur difficult to hear at first. Over time, changes in the pulmonary circulation can lead to pulmonary hypertension developing, which alters the pressures around the defect and increases turbulent flow across the VSD. This makes the murmur become audible later.

So the idea is that the murmur emerges as pulmonary hypertension develops and the pulmonary pressures interact with the defect to produce measurable turbulent flow.