CPB circuit The CPB circuit contains a roller pump, and a hollow fiber membrane oxygenator microporous polypropylene (PPL), with a rigid venous reservoir. The bypass circuit will be prepared using 1,400 ml of saline solution 0.9%, 100 ml Albumin 20% and 5,000 units of Heparin. After heparinization, the surgeon will make cannulation of the aorta artery followed by cannulation of veins upper and lower Cavas, respectively. During CPB, the patient's temperature is maintained at 35 ° C with the valve replacement procedure performed with intermittent cross-clamping. The pH-stat system for analysis of blood gases is utililizado to control the acid-base balance in all patients. The target blood flow during cardiopulmonary bypass would be 2.4 liters / min / m2 and is increased to 3.2 liters / min / m2 in order to maintain the central venous oxygen saturation above 75%. The activated clotting time will be at least 480 s during the infusion. The fresh gas flow rate in the supply of gas to the oxygenator will be adapted by the perfusionist to maintain arterial carbon dioxide from 30 to 35 mmHg. The concentration of oxygen in the gas mixture delivered to the oxygenator will be 30-80% depending on the partial pressure of arterial oxygen at a partial pressure of oxygen above the target of 80 mmHg measured at oxygenated blood flow.