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Background and aim: The heart secretes brain natriuretic peptide (BNP) in response to myocardial stretch. The aim of this study was to determine whether adverse effects after cardiac surgery were associated with higher serum BNP levels pre-operatively. Methods: One hundred and thirty-five patients undergoing various cardiac procedures were included in the study, and N-terminal pro-BNP (NT-pro-BNP) was measured pre-operatively. Post-operative complications were defined as follows: (i) a post-operative length of stay in the intensive care unit (ICU) exceeding 48 h; (ii) mortality at 28 days; (iii) the need for inotropic agents and/or intra-aortic balloon pump (IABP); and (iv) renal failure. Serum NT-pro-BNP values were compared for patients with and without complications. The serum NT-pro-BNP level was also correlated with the euroSCORE and ejection fraction (EF). Results: Pre-operative serum NT-pro-BNP levels were significantly higher in patients with an ICU length of stay of more than 2 days or death prior to post-operative day 28 (3118 ng/l vs. 705 ng/l; P < 0.001). Pre-operative serum NT-pro-BNP levels were also significantly higher in patients needing inotropic agents (2628 ng/l vs. 548 ng/l; P < 0.001) or IABP insertion (3705 ng/l vs. 935 ng/l; P = 0.001) or developing renal failure (2857 ng/l vs. 945 ng/l; P < 0.001) post-operatively. The correlation between the serum NT-pro-BNP level and euroSCORE was good ( r = 0.658; P < 0.001). The receiver operating characteristic (ROC) curves were used to assess the ability of serum NT-pro-BNP, euroSCORE and EF to predict outcome after cardiac surgery. This revealed an area under the ROC curve for the length of stay in the ICU or mortality at 28 days of 0.829 for serum NT-pro-BNP, 0.814 for euroSCORE and 0.328 for EF assessed by transesophageal echocardiography, indicating that the pre-operative serum NT-pro-BNP level is a good prognostic indicator for outcome after cardiac surgery. Conclusion: Serum NT-pro-BNP is a good predictor for complications after cardiac surgery, and is as good as euroSCORE and better than EF. [ABSTRACT FROM AUTHOR]