A 10-day-old infant is brought to the emergency room of your hospital by his mother with a history of progressive irritability and poor breastfeeding. On history, the infant was born by uncomplicated spontaneous vaginal delivery at 40 weeks gestation following a completely unremarkable pregnancy. Birth weight was 3.5 kg. The infant was well after birth and breast feeding was initiated by his mother without any problems. He was discharged home on day 2 of life. Over the subsequent days, the infant had increasing irritability and poor feeding; his mother describes him as having more difficulty at the breast, sucking for only a few seconds and then seeming short of breath. She also notices that he seems to be getting more tired and that his lips turn purple during feeding. In the emergency room, the baby is irritable and cyanotic-looking. Vital signs show a respiratory rate of 36 breaths per minute, heart rate of 195 bpm; BP 75/30 mmHg; oxygen saturation 75% on room air. He is noted to be warm and well perfused, but persistently cyanotic. On exam, he has palpable femoral pulses bilaterally, and normal breath sounds. Lung fields are clear to auscultation. He has a harsh systolic murmur best appreciated on the left upper sternal border. You provide 100% oxygen by face mask and order bloodwork, EKG and a chest X-ray.