MRCP UK EXAMINATIONS

week-old FT newborn. SOB with feeds. Mom had no prenatal care. Physical examination is remarkable for a blood pressure of 100/60 mmHg in the right arm, redundant skin overlying the posterior neck, and edema of the lower extremities. MURMUR:Gallop rhythm and a regurgitant murmur at the mid-precordium. Femoral pulses are diminished. Subcostal retractions. Rales on auscultation of the lungs. MOST appropriate next step in the evaluation of this infant is: