A 68-year-old woman with ischaemic cardiomyopathy (LVEF 30%), NYHA class II symptoms, normal renal function and potassium 4.4 mmol/L is already on maximally tolerated ACE inhibitor, beta blocker and SGLT2 inhibitor. Her blood pressure is 118/70 mm Hg. What is the next best evidence-based pharmacologic step?