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Background: Delirium is a common postoperative complication after cardiac surgery. The relationship between delirium and cardiac function has not been fully elucidated. Aims: The aim of this study was to identify the association between preoperative cardiac function and delirium among patients after cardiac surgery. Methods: We prospectively recruited 635 cardiac surgery patients with a planned cardiac intensive care unit admission. Postoperative delirium was diagnosed using the confusion assessment method for the intensive care unit. Preoperative cardiac function was assessed using N-terminal prohormone of brain natriuretic peptide (NT-proBNP), New York Heart Association functional classification and left ventricular ejection fraction. Results: Delirium developed in 73 patients (11.5%) during intensive care unit stay. NT-proBNP level (odds ratio (OR) 1.24, 95% confidence interval (CI) 1.01–1.52) and New York Heart Association functional classification (OR 2.34, 95% CI 1.27–4.31) were both independently associated with the occurrence of delirium after adjusting for various confounders. The OR of delirium increased with increasing NT-proBNP levels after the turning point of 7.8 (log-transformed pg/ml). The adjusted regression coefficients were 1.19 (95% CI 0.95–1.49, P =0.134) for NT-proBNP less than 7.8 (log-transformed pg/ml) and 2.78 (95% CI 1.09–7.12, P =0.033) for NT-proBNP greater than 7.8 (log-transformed pg/ml). No association was found between left ventricular ejection fraction and postoperative delirium. Conclusion: Preoperative cardiac function parameters including NT-proBNP and New York Heart Association functional classification can predict the incidence of delirium following cardiac surgery. We suggest incorporating an early determination of preoperative cardiac function as a readily available risk assessment for delirium prior to cardiac surgery. [ABSTRACT FROM AUTHOR]