An 8-year-old boy is brought to a physician because of palpitation, fatigue, and dyspnea. On examination, a continuous machinery murmur is heard best in the second left intercostal space and is widely transmitted over the precordium. The most likely diagnosis is

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

Answer: (A)

The key idea is that a continuous “machinery” murmur that is best heard at the left second intercostal space and radiates widely across the precordium points to patent ductus arteriosus. This defect persists when the small vessel connecting the aorta to the pulmonary artery fails to close after birth, creating a continuous left-to-right shunt throughout both systole and diastole. The high aortic pressure drives blood into the pulmonary circulation all through the cardiac cycle, producing a murmur that is present continuously and can be heard best in that left upper chest location with wide transmission across the chest.

Clinically, PDA leads to increased pulmonary blood flow, which can cause fatigue, dyspnea, and palpitations as the heart works harder to handle the extra load. The murmur’s quality and location help distinguish it from other congenital lesions: a holosystolic murmur at the lower left sternal border suggests a ventricular septal defect; a fixed split S2 with a systolic murmur at the left upper sternal border suggests an atrial septal defect; a systolic ejection murmur best at the right second intercostal space points toward congenital aortic stenosis.