A Study Comparing Blood Flow and Clinical and Safety Effects of the Addition of Natrecor (Nesiritide), Placebo or Intravenous Nitroglycerin to Standard Care for the Treatment of Worsening Congestive Heart Failure.

Inclusion Criteria:

• Patients with dyspnea (difficulty breathing and shortness of breath) at rest, while supine, or immediately upon minimal activity such as talking, eating, or bathing
• having evidence of heart disease, rather than pulmonary disease, as the primary cause for the dyspnea (by demonstrating at least two of the following: jugular venous distension, paroxysmal nocturnal dyspnea or 2-pillow orthopnea within 72 hours before the start of study drug, abdominal discomfort due to hepatosplanchnic congestion, chest x-ray with findings indicative of heart failure)
• having elevated cardiac filling pressures either by clinical estimate in non-catheterized patients, or a measured pulmonary capillary wedge pressure (PCWP) >= 20 mm Hg in catheterized patients
• requiring hospitalization and intravenous therapy for at least 24 hours for the treatment of acutely decompensated heart failure.

Exclusion Criteria:

• NPatients having systolic blood pressure consistently less than 90 mm Hg
• having cardiogenic shock (a sudden decrease in blood pressure that results in decreased perfusion of body tissues and organs), volume depletion, or any other clinical condition that would contraindicate the administration of an intravenous agent with potent vasodilating properties
• having their most recent pulmonary capillary wedge pressure (PCWP) < 20 mm Hg within 24 hours before randomization
• having a clinical status so acutely unstable that the potential subject could not tolerate placement of a right heart catheter or the 3-hour placebo period
• unable to have intravenous nitroglycerin withheld (e.g., intravenous nitroglycerin for management of an acute coronary syndrome).