A 60-year-old man with heart failure states that he becomes "a bit short of breath" after climbing a flight of stairs. His ejection fraction is 40%. Current medications include lisinopril 5 mg daily, metoprolol XL 100 mg daily, aspirin 81 mg daily, furosemide 40 mg daily, and digoxin
250 mcg daily. All vital signs and laboratory values are stable and within normal limits. Which of the following recommendations would be most appropriate at this time?