A 67-year-old white woman presents with a 6-month history of shortness of breath, initially with exertion, but now also at night and when lying down. She has no history of serious illness. Examination shows jugular venous distention. Crackles are heard at both lung bases. There is 2+ pitting edema of the lower legs and ankles. Echocardiography shows a left ventricular ejection fraction of 35%. Which of the following is the most appropriate drug to reduce mortality from her condition?