 All research subjects will be adults admitted to the heart failure ICU with acute decompensated heart failure and requiring monitoring of their heart function using a catheter that is placed in the pulmonary artery which is a blood vessel. In this situation, use of the pulmonary artery catheter,or PAC, is considered standard clinical care. It is not a research procedure. The PAC would be used even if you were not participating in this research project. 