A 52-year-old man from Delhi presents with progressive dyspnea on exertion for 6 months and orthopnea. On examination, he has an early diastolic decrescendo murmur at the left sternal border, a wide pulse pressure (systolic 160 mmHg, diastolic 50 mmHg), and a collapsing pulse. Chest X-ray shows cardiomegaly and pulmonary edema. Transthoracic echocardiography confirms severe aortic regurgitation with an ejection fraction of 45%. He is currently on amlodipine 5 mg daily. What is the most appropriate next step in management?