The primary objective of this study is to establish that Nesiritide (Natrecor) is effective in reducing pulmonary hypertension (PHTN) acutely as measured by a 20% reduction in the mean pulmonary arterial (PA) pressure. The secondary objectives will include: improvement in pulmonary vascular resistance (PVR), patient symptoms, exercise tolerance, frequency of toxicity, and surgeon's willingness to proceed with operation.

The patient population recruited for this study will include patients being considered for cardiothoracic surgery, as treatment for their cancer, who have evidence of PHTN documented by 2-dimensional and Doppler echocardiography (2D-Echo) uncovered during their pre-operative evaluation for malignancy. Eligible patients include those who have normal LV systolic function with PHTN by Doppler echocardiography, defined as a peak tricuspid velocity of 2.5m/sec or greater without evidence of significant valvular disease. An evaluation for pulmonary hypertension by 2D-Echo will have already been completed by the time the patient is considered for this study.

Inclusion Criteria:

• Age 18 to 85 years old
• Pulmonary Hypertension (PHTN) documented by Doppler echocardiography
• Evidence of underlying lung disease by history and physical and/or chest x-ray and/or pulmonary function testing (PFT's)
• Able to sign informed consent
• Patient being considered for Cardiothoracic Surgery

Exclusion Criteria:

• Patients with clinically significant hypotension (defined as a systolic blood pressure (SBP) <90)
• Active infection/sepsis
• Creatinine greater than 3.0 mg/dl
• LV ejection fraction < 40% (must be done with in the last 30 days prior to signing consent)
• Significant valvular disease as a cause for the PHTN.
• Severe Thrombocytopenia (as defined by platelets less than 20,000) or INR > 1.6
• Hypersensitivity to nesiritide or any of it's components.