The purpose of the study is to compare the effects of conivaptan and diuretics on renal blood flow and neurohormones.

1. To define the hemodynamic, neurohormonal and renal responses to intravenous conivaptan in patients with chronic stable heart failure (HF), and compare these responses to those after intravenous furosemide.
2. To define the hemodynamic, neurohormonal and renal responses to the combination of the two drugs (conivaptan and furosemide).

Inclusion Criteria:

• Have a diagnosis of chronic congestive heart failure of any etiology
• Be between 18-80 years of age
• Able to provide consent
• Have a documented left ventricular ejection fraction within the last year of < 40%
• On a stable dose (no changes within 2 weeks) of 40 mg or greater daily dose of furosemide or its equivalent
• On standard HF therapy medications (ACEI or ARB and beta-blocker unless contraindicated)
• Have an estimated glomerular filtration rate (GFR) of 30 ml/minute or greater (based on the Cockcroft Gault calculation)
• Have a hemoglobin of > 10 grams/dl
• Have a negative urine pregnancy for women of childbearing years only

Exclusion Criteria:

• Acute coronary syndrome within 1 month
• Systolic blood pressure less than or equal to 90 mmHg at time of enrollment
• Poor peripheral venous access
• Severe concomitant disease which deemed by the investigator would render them unsuitable for this trial
• Allergy or contraindication to the use of iothalamate, PAH - Specifically any allergies to iodine or iodine containing products, history of asthma and hay fever which deemed by the investigator would render them unsuitable for this trial