Problem: A 2-month-old girl is seen in the pediatric office for her well-child checkup. Her mother reports she previously breast-fed 20 minutes every 2 to 3 hours but now is requiring 40 minutes to breast-feed with a frequency of every 4 hours. She sweats with all the feeds but does not turn blue. She continues to produce her normal quantity of wet diapers and stools. On physical examination, the girl is awake, alert, has subdiaphragmatic retractions, abdominal breathing; her respiratory rate is 58 breaths/min and the pulse is 175 beats/min. Oxygen saturation measured on her right hand is 98%. You hear a 2/6 holosystolic murmur along the left sternal border. The murmur is harsh, low-pitched, and does not radiate. The lung fields have scattered crackles bilaterally.