Practice question

A 68-year-old man with a history of heart failure with reduced ejection fraction (EF 30%) presents with increasing dyspnea on exertion. He is on an ACE inhibitor, beta-blocker, and loop diuretic at maximally tolerated doses. Blood pressure is 112/68 mm Hg, potassium 4.6 mEq/L, and eGFR 55 mL/min/1.73 m². Which medication should be added to improve morbidity and mortality?