 Patients meet the inclusion criteria and agree to sign an informed consent will be randomly assigned into the control group or erythropoietin group.Interventions will be applied 1 day24hrs before the cardiac surgery. Blood and Urine samples will be collected after the surgery. By using the criterion given by KDIGO2012 and testing the biomarkers for acute kidney injury, we hope to find out if there is an association between erythropoietin administration and the occurence of acute kidney injury. 