A previously healthy 58 years old man is admitted to the hospital because of an acute inferior myocardial infarction. Within several hours, he becomes oliguric and hypotensive (blood pressure is 90/60 mmHg). Inseion of a pulmonary aery (Swan-Ganz) catheter reveals the following pressures: pulmonary capillary wedge-4 mm Hg; pulmonary aery- 22/4 mmHg: and mean right atrial- 11 mmHg. This man would best be treated with :