A 65-year-old man with a history of hypertension and ischemic heart disease presents to the emergency department with worsening shortness of breath, orthopnea, and peripheral edema. On examination, he has elevated jugular venous pressure, bilateral basal crackles, and pitting edema in the lower limbs. An echocardiogram shows an ejection fraction of 35%. What is the most appropriate initial management step for this patient?