A 3-month-old male infant born to non-consanguineous parents presents with poor feeding and failure to thrive. On examination, he has a hyperdynamic precordium, a wide pulse pressure (systolic 95 mmHg, diastolic 40 mmHg), and a continuous 'machinery' murmur best heard at the left infraclavicular region. Chest X-ray shows cardiomegaly with pulmonary plethora. What is the most appropriate next step in management?