A 72-year-old man is evaluated during a routine examination. He has no symptoms or significant medical history. He is active and exercises regularly. He does not take any medications.

On physical examination, blood pressure is 135/70 mm Hg, pulse rate is 82/min, and respiration rate is 17/min. Cardiac examination reveals a grade 3/6 apical holosystolic murmur.

Echocardiogram shows severe mitral regurgitation and a left ventricular ejection fraction of 45% without evidence of regional wall motion abnormalities.

Which of the following is the most appropriate management?