A 3-year-old boy from Delhi is brought to the pediatric clinic by his mother with a complaint of recurrent respiratory tract infections and poor weight gain since infancy. On examination, he is found to have a continuous 'machinery' murmur best heard at the left infraclavicular region. His peripheral pulses are bounding with a wide pulse pressure (BP 110/40 mmHg). Chest X-ray shows cardiomegaly with pulmonary congestion. Echocardiography confirms a left-to-right shunt at the ductal level. What is the most likely diagnosis?