An infant has a continuous-machine type of murmur best heard at the left upper sternal border. These clinical findings are consistent with which congenital heart defect?

The continuous-machine type of murmur described in the question is characteristic of a patent ductus arteriosus (PDA). This murmur occurs due to the abnormal persistence of the ductus arteriosus, which connects the pulmonary artery to the aorta during fetal development. After birth, when the ductus normally closes, the PDA allows blood to flow continuously from the aorta into the pulmonary artery, creating a characteristic "machine-like" sound that can be best auscultated at the left upper sternal border.

In the case of the PDA, this abnormal flow leads to increased blood flow to the lungs and potential congestive heart failure symptoms in the infant. The location of the murmur aligns with the anatomic position of the ductus arteriosus, further supporting that this defect leads to such a specific auscultation finding.

Other congenital heart defects can produce murmurs, but they do not present the same continuous pattern as seen with PDA. For example, an atrioventricular canal defect can lead to a variety of murmurs depending on the severity and timing of left-to-right shunting, yet it lacks the distinctive continuous nature. An atrial septal defect might generate a systolic ejection murmur due to increased flow across