Acute normovolemic hemodilution (ANH) is performed as a blood conservation technique during surgical procedures with high risk for significant blood loss. It is done by taking out some of the patients blood before surgery actually begins and storing this blood inside of the operating room and giving it back to the patient at the end of surgery when most of the expected surgical bleeding has already occurred. This practice reduces the amount of bleeding that occurs after surgery and also reduces the amount of blood transfusions given to the patient after surgery. Transfusion of blood products from the blood bank may cause problems such as transfusion reactions and infections like hepatitis, and also increases cost. 3 meta-analyses and several smaller trials have shown improvement in blood transfusion rates with the use of ANH, however there is no evidence of improvement in other complication rates, morbidity and mortality, length of stay or cost. In most types of surgery, when ANH is done, large volumes of IV fluids are given to the patient to prevent a drop in circulatory volume and blood pressure. However during heart surgery, this can cause significant levels of hemodilution in addition to that caused by use of the heart-lung machine. In order to minimize hemodilution when ANH is performed during heart surgery, a smaller amount of IV fluids are given to the patient after blood is drawn. Vasoactive medications are then administered to prevent the blood pressure from dropping. Kidney injury is a recognized complication that may occur after heart surgery. It may be caused by low blood volume, low blood pressure and anemia. It is not known whether performance of ANH and use of the heart-lung machine may increase risk for kidney injury. Kidney injury is associated with increased risk for other medical complications and death. This increased risk for kidney injury arising from ANH has not been evaluated. This study will therefore compare patients treated with ANH to those not treated with ANH to determine whether there is an increased risk for kidney injury with the use of ANH.