MSRA-0014

A 63-year-old male is being seen in the nurse-led heart failure clinic. Despite being on current treatment with furosemide, bisoprolol, enalapril, and spironolactone, he continues to experience breathlessness with minimal exertion. Upon examination, his chest is clear to auscultation and there is minimal ankle edema. Recent test results show sinus rhythm with a rate of 84 bpm on ECG, cardiomegaly with clear lung fields on chest x-ray, and an ejection fraction of 35% on echo. Isosorbide dinitrate with hydralazine was recently attempted but had to be discontinued due to side effects. What additional medication would be most effective in alleviating his symptoms?