Review Question - QID 217028

An 84-year-old man presents to the emergency department with a 1-week history of shortness of breath while walking. One week ago, he returned from a cross-country road trip. At the beginning of his road trip, he experienced an upper respiratory tract infection that self-resolved. He otherwise has not had other symptoms or anything else he thinks is related to his presentation. He has a past medical history of diabetes controlled with metformin and a coronary bypass surgery 8 years prior. He smokes 1 pack of cigarettes a day for the past 50 years. On physical exam, his temperature is 98.6°F (37°C), blood pressure is 86/45 mmHg, pulse is 133/min, and respirations are 22/min with an oxygen saturation of 98% on room air. Physical exam reveals jugular venous distension, and auscultation is notable for distant heart sounds. His abdomen is soft and nontender. Weak pulses are palpated in the upper and lower extremities. An ECG is obtained and shown in Figure A. The patient is given 2 liters of normal saline with minimal change in his vital signs. The patient subsequently appears more somnolent. Further testing is ordered. Which of the following is most likely to improve this patient's symptoms?