The third method, estimated Continuous Cardiac Output (esCCO), uses sensors placed on the patient's finger, arm and chest to calculate Pulse Wave Transit Time (PWTT); the time it takes for the heart beat pulse to travel through the patient's body. The esCCO system is FDA approved for safety and efficacy to measure noninvasive blood pressure and pulse oximetry. The purpose of this study is to assess whether the PSTT calculation provides a cardiac output measure that is comparable to the other methods.