The purpose of this pilot study is to compare the clinical effects, safety profile, and economic impact of standard therapy plus NatrecorÂ® (nesiritide, a recombinant form of the natural human peptide normally secreted by the heart in response to heart failure) to standard therapy plus placebo in patients who present to the Emergency Department with worsening congestive heart failure (CHF) and are treated in the Emergency Department /Observation Unit.