A 78-year-old woman is admitted to the ICU with an anterior myocardial infarction. She is treated with aspirin, thrombolytic therapy, and nitrates. Her clinical course is uneventful until the third hospital day, when she has sudden onset of shortness of breath. Her BP is 95/55 mm Hg, pulse rate is 124 beats/min, and respiratory rate is 32 breaths/min. Cardiovascular examination reveals jugular venous distention, soft heart sounds, and a pansystolic murmur. She has bibasilar crackles. A chest radiograph shows pulmonary edema. Her ECG shows sinus tachycardia and an evolving anterior myocardial infarction. A pulmonary artery catheter is inserted, and the following readings are obtained: right atrium pressure, 6 mm Hg (56% O2 saturation); right ventricular pressure, 40/6 mm Hg (55% O2 saturation); pulmonary artery pressure, 40/23 mm Hg (mean, 30 mm Hg; 57% O2 saturation); pulmonary artery occlusion pressure, 24 mm Hg (v waves to 40); and cardiac output, 3.5 L/min. Which of the following is most appropriate at this time?