In all patients, a median sternotomy will be performed. CPB will be initiated after full heparinization in a dose of 300-400 I.U to achieve a n ACT( activated clotting time) of 450 sec or 3 times baseline reading followed by the standard aorta-bicaval cannulation. A membrane oxygenator (Mini-max Plus; Medtronic Inc., Anaheim, CA) and a non-pulsatile roller pump (model 10.10.00; Stôckert Instruments; Munich, Germany) will be used. Venting of the left heart will be performed with a left atrial vent inserted through a small incision at the interatrial septum. Priming fluids consist of lactated Ringer's solution supplemented with heparin. Fresh whole blood was added to the priming solution in appropriate amounts to achieve a hematocrit of 20% to 22% during CPB ( cardiopulmonary bypass). Moderate hypothermia (26°C to 28°C) will be used during CPB.