A 35-year-old man with a history of acute rheumatic fever presents with signs of mitral regurgitation and aortic stenosis. Clinical examination and chest X-ray suggest left ventricular hypertrophy and left atrial enlargement. The patient is being evaluated for suitability for surgical intervention. Which investigation is most appropriate to assess the morphology of the aortic valve, degree of calcification, and suitability for valve repair versus replacement?