Determination of cardiac output (CO) is often desirable for assessing a patient's hemodynamic condition during the surgery requiring cardiopulmonary bypass. However, the current methods of continuous CO measurement are still based on invasive technique, such as thermodilution via pulmonary artery catheter (Swan-Ganz), transpulmonary thermodilution via PiCCO kit, or pulse contour analysis via arterial line (FloTrac or PiCCO). Noninvasive CO measurement to all patients is currently impractical, because most measurement methods available are based on invasive techniques. However, two developing trends for this kind of monitor had occurred. There are one shifting toward noninvasive technologies and the other trend toward continuous measurement rather than intermittent measurement. Therefore, continuous CO (CCO) monitoring with less invasive would be desirable.