The relationship between peripheral venous saturation and central hemodynamics (including right and left heart filling pressures and cardiac output), mixed venous oxygen saturation, and contemporary biomarkers of heart failure is not clear. We aim to determine the relationship between mixed venous, central venous, and peripheral venous oxygen saturation in patients with advanced (class III or IV) heart failure. We will determine the relationship between cardiac output measured via thermodilution and the Fick equation calculated using concurrent oxygen saturations from the distal PA, central vein, and peripheral vein. We also aim to examine the relationship of selected cardiac biomarkers with cardiac filling pressures and cardiac output over time in patients with decompensated heart failure.

The following inclusion criteria will be utilized:

1. Age>21
2. PA-catheter insertion for therapy of congestive heart failure decided upon by the attending cardiologist

The following will be considered as exclusion criteria for this study

1. Known or suspected septic shock or bacteremia
2. Active bleeding or HCT<24% at baseline
3. Arterial oxygen saturation <90% at baseline despite supplemental oxygen therapy.
4. Previous difficulty with venipuncture of upper extremity veins or the presence of a surgical arteriovenous fistula for hemodialysis
5. Insertion of the PA catheter through the femoral vein
6. Subjects unwilling or unable to provide written consent

The study population will consist of 30 patients admitted to the Massachusetts General Hospital Coronary Care Unit (CCU) for PA catheter-directed therapy for advanced heart failure. Only patients for whom the attending cardiologist has already decided upon PA-catheter insertion will be recruited for the study.

Potential subjects will be identified by the CCU attending cardiologist, and a study nurse will review each patient for the exclusion criteria as above. Final decisions on patient eligibility will be made by Dr. Wang.