In order to measure intraoperative CO values, we will utilize the pulmonary artery (PA) catheter that was placed at the beginning of the surgery.. The patient will have a catheter placed in the right side of the neck that will travel through the heart and into a branch of the artery that goes from the heart to the lungs. This catheter will have the ability to measure the amount of blood that is pumped from the heart per minute. At the same times that the pressure in the aorta is measured (as above), the amount of blood that is pumped from the heart per minute will be measured.