We propose to compare measurement of cardiac output made with the Conmed ECOM 6-3D endotracheal tube to those made with a pulmonary artery catheter using. We will do correlation studies of cardiac output against those performed using the standard thermodilution technique in patients, who in the normal course of their clinical care, are having cardiac outputs measured by the thermodilution technique. We will compare cardiac output measured by impedance cardiography to transit time measurements.