A 72-year-old woman with hypertension and diabetes mellitus type 2 is found to have a left ventricular ejection fraction (LVEF) of 38% on routine echocardiography during evaluation for exertional dyspnea. She denies orthopnea, paroxysmal nocturnal dyspnea, or peripheral edema. Physical examination is unremarkable except for mild hypertension (BP 148/92 mmHg). Serum creatinine is 1.1 mg/dL, potassium 4.2 mEq/L. She is currently on amlodipine and metformin. What is the most appropriate next step in management?