Review Question - QID 109796

A 2-month-old infant presents for a well-child visit. The mother, a recent immigrant from El Salvador, delivered her child in the United States with an unclear prenatal history. Her child sleeps throughout the day and night but has also had 3 "flu" episodes during which the infant coughed and felt feverish. She managed each episode using traditional non-pharmacological remedies. Because the baby sleeps so much, he rarely breastfeeds. His temperature is 99.5°F (37.5°C), blood pressure is 70/30 mmHg, pulse is 160/min, respirations are 27/min, and oxygen saturation is 91% on room air. On physical exam, the patient is the 5th percentile for weight and height. He has a hyperinflated thorax and is tachypneic. Auscultation of the heart reveals a holosystolic murmur heard at the left lower sternal border and a diastolic rumble at the apex. Chest radiography is shown in Figure A. Which of the following is the most likely diagnosis?