Based on the evidence from cell culture study and animal study in the literature, we hypothesize that Cyr61 is rapidly increased in the urine after AKI. We thus design this project to evaluate study the diagnostic role and clinical application of Cyr61 in AKI. We will conduct a prospective cohort study to evaluate the changes of urinary Cyr61 in patients undergoing cardiac surgery. Cyr61 may serve a good biomarker for the early diagnosis of patients with AKI, either singly or in combination with NGAL. By the way, we also try to correlate the changes in those biomarker with a potential new tool：harmonic analysis of arterial pressure pulse waves. We have special interest in following the time course of changes in biomarker and correlate with changes in pulse analysis. Physiological parameters of vascular compliance and regional blood oxygen saturation will be correlated concurrently. It is hoped that early detection of AKI will lead to earlier intervention, thus enhancing our ability to develop beneficial therapies.