On a routine neonate examination, a grade IV/VI holosystolic murmur is heard in the 3rd-4th left intercostal space in the parasternal line. The murmur is most likely that of

• A. Atrial septal defect
• B. Ventricular septal defect
• C. Patent ductus arteriosus
• D. Mitral stenosis

Answer: (D)

A murmur that is holosystolic and heard along the left lower sternal border in a neonate is most consistent with a ventricular septal defect. The entire systole is spent pushing blood from the left ventricle to the right through a defect in the interventricular septum, producing a holosystolic murmur that is often loud and best heard at the left parasternal area around the 3rd–4th intercostal space.

Atrial septal defect usually presents with a systolic ejection murmur at the left upper sternal border and a fixed splitting of the second heart sound, not a holosystolic murmur. Patent ductus arteriosus creates a continuous “machinery” murmur best heard at the left infraclavicular region, not confined to systole. Mitral stenosis generates a diastolic rumble at the apex with an opening snap, which is not the holosystolic pattern described in this neonate.