A 72-Year-Old Woman Comes to the Office for Follow-Up of Shortness

A 72-year-old woman comes to the office for follow-up of shortness of breath.  For the last year, the patient has had increasing dyspnea on exertion and can now walk only 2-3 blocks at a slow pace.  She has had no associated chest pain or lightheadedness.  The patient was seen at an urgent care facility a month ago and was found to have bibasilar crackles and 1+ bilateral pedal edema.  She was started on daily furosemide, with significant improvement in her symptoms, and was instructed to see her regular physician for further evaluation.  Medical history is notable for hypertension treated with amlodipine and spironolactone, and the patient has no history of myocardial infarction or stroke.  She is a lifetime nonsmoker and does not use alcohol.
Blood pressure is 125/70 mm Hg and pulse is 75/min and regular.  Oxygen saturation is 98% on room air.  BMI is 24 kg/m².  Cardiac auscultation shows an S4 and no murmurs.  Lung sounds are normal.  There is no peripheral edema.
ECG shows normal sinus rhythm with left ventricular hypertrophy.  Complete blood count and basic metabolic panel are unremarkable.  Transthoracic echocardiogram shows left atrial enlargement, left ventricular hypertrophy, left ventricular ejection fraction of 65%, and pulmonary artery systolic pressure of 50 mm Hg.
Which of the following is most likely to improve quality of life in this patient?

A) Beta blocker therapy
B) Exercise training
C) Long-acting nitrate therapy
D) Low-carbohydrate, high-protein diet
E) Phosphodiesterase-5 inhibitor therapy