Patent ductus arteriosus (PDA) characteristically presents with which murmur and shunt pattern?

• A. Harsh holosystolic murmur at the apex
• B. Continuous machine-like murmur; left-to-right shunt; noncyanotic
• C. S4 gallop
• D. Diastolic murmur at the left upper sternal border

Answer: (B)

PDA is identified by a continuous, machinery-like murmur that persists through both systole and diastole, best heard at the left infraclavicular area. The defect creates a left-to-right shunt from the aorta to the pulmonary artery, so blood flows systemically into the pulmonary circulation year-round, which typically keeps the patient noncyanotic in the early stages. The continuous flow explains why the murmur spans the entire cardiac cycle, unlike murmurs confined to systole or diastole. In contrast, a harsh holosystolic murmur at the apex points to mitral regurgitation, an S4 gallop reflects a stiff or hypertrophic ventricle, and a diastolic murmur at the left upper sternal border suggests other lesions like regurgitation—none of which match the PDA pattern.