The application of acute Normovolemic Hemodilution in cardiac surgery can effectively reduce perioperative blood transfusion, reduce postoperative complications and mortality, and is a low-cost, operable and effective blood protection measure.For the application of Acute Normovolemic Hemodilution in heart surgery, we still face an urgent problem: to what extent can Acute Normovolemic Hemodilution achieve better "blood saving effect", that is, whether a large number of Acute Normovolemic Hemodilution can reduce perioperative blood transfusion to a greater extent

Inclusion Criteria:

• （1）18-75years old;（2）elective cardiac surgery under cardiopulmonary bypass; （3）Preoperative hemoglobin (Hb) ≥ 12g/dl; (4) Transfusion Risk Understanding Scoring Tool (TRUST) ≥ 2 (possibility of blood transfusion ≥40%).

Exclusion Criteria:

• （1）congenital heart disease、Cardiac tumor、aortic dissection、heart transplantation（2）Low body weight（<50 kg）;（3）preoperative shock；（4）myocardial infarction within 3 months before surgery；（5）ischemic heart disease;Left main coronary artery stenosis >70%;Severe aortic stenosis (area < 0.7cm2);Severe changes in left ventricular function (ejection fraction <30%, requiring vasoactive agents to assist circulation);（6）severe carotid artery stenosis (>70% or with symptoms);（7） kidney failure (blood creatinine level >442 mmol/L) or dialysis treatment;（8） serum albumin level (ALB) is less than 25 g/L.（9） international standardized ratio (INR) >1.5 or platelet count <100 103/mm3;（10）Inherited/acquired coagulation function defect;（11）contagious or infectious diseases;（12） patient or family members refused to participate in research;（13）refused to infusion of autologous blood or allogeneic blood products