Comparing the Effects of Conivaptan and Diuretics on Plasma Neurohormones and Renal Blood Flow in Patients With Chronic Congestive Heart Failure

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