A 72-year-old female patient suffers from a long-standing heart failure. She presents to the hospital with a cough and dyspnea on exertion for 1 week. Her symptoms worsen at night, and she has noticed that her sputum is pink and frothy. Chest auscultation reveals bilateral fine crepitations over the lung bases. The physician prescribes a drug that reduces preload. Which of the following is the most likely drug prescribed by the physician?