A 35-year-old woman with recently diagnosed nonischemic systolic heart failure and a left ventricular ejection fraction of 30% presents 1 week after hospital discharge with a new cough, increased exertional dyspnea, and peripheral edema. Medications are lisinopril (5 mg/d) and furosemide (40 mg/d).

On physical examination, blood pressure is 100/70 mm Hg, pulse rate is 98/min and regular, respiration rate is 13/min, and oxygen saturation on ambient air is 96%. Estimated central venous pressure is 15 cm H2O. Her weight has increased by 2.3 kg (5 lb). Cardiac examination reveals a grade 2/6 holosystolic murmur at the apex and an S3. Extremity examination reveals bilateral peripheral pitting edema.

Her electrocardiogram shows sinus rhythm and is unchanged from baseline. Serum electrolyte levels and kidney function tests are normal.

In addition to a low-sodium diet, which of the following is the most appropriate management?