We will compare three methods for measuring cardiac output: esCCO, PAC, and ECOM. Cardiac output is an important physiological parameter that must be monitored closely during surgery and during an Intensive Care Unit (ICU) stay. The use of a pulmonary artery catheter (PAC) has been the gold standard for accurate cardiac output (CO) measurement. This method requires a catheter to be inserted into the pulmonary artery and cardiac output is indicated by the speed that a temperature gradient dissipates. While the use of the pulmonary artery catheter is widespread, inserting the pulmonary artery catheter is risky, time consuming and requires a high level of skill. For these reasons, new devices have been developed to measure cardiac output.