A 1-month-old girl is brought to the physician for a well-child examination. She was born at term following an uncomplicated delivery. Pulse oximetry is 98% on room air. Auscultation of the chest demonstrates a to-and-fro murmur. Pulse pressure is increased. Peripheral pulses are 4+ in all extremities. Which of the following is the most likely explanation for these findings?
Extra-cardiac left-to-right shunt
Extra-cardiac right-to-left shunt
Intra-cardiac atrial left-to-right shunt
Intra-cardiac ventricular left-to-right shunt
Intra-cardiac ventricular right-to-left shunt
