The study hypothesis is that the efficacy and safety profile of Natrecor® may be conducive to its early administration for acute treatment of heart failure in the Emergency Department and that in addition to standard care, may make it possible to further reduce hospital admissions or the severity of the patient's condition at the time of admission. Natrecor® 1.5 mg for injection made up to final concentration of 0.3 mg/mL with 5% dextrose in water, or placebo. Dispensed as an intravenous bolus of 2 mcg/kg over approximately 60 seconds, immediately followed by a fixed-rate infusion of 0.01 mcg/kg/min for at least 12 hours.