ABSTRACT Introduction: Acute kidney injury (AKI) is a marker of poor prognostic after cardiac surgery. Recent studies suggest that hyperchloraemia may be significantly associated with the development of this complication. However, there is little information regarding the prevalence of abnormal chloride concentrations after cardiac surgery and its relationship to postoperative AKI. On the other hand, the use of inotropes in postoperative cardiac surgery patients has been associated with several types of adverse outcomes. Aims: Determine the relationship between hyperchloraemia and AKI in patients following cardiac surgery and to evaluate whether variables associated with tissue hypoperfusion or the use of inotropes are related to the development of this complication. Methods: An observational cohort study was performed at a hospital with a focus on high-complexity cardiovascular patients. We included 464 adult patients who had undergone heart surgery. Results: AKI was found in 12.7% of the patients. Additionally, 76% had had hyperchloraemia at least once during the first 48 h after surgery. The highest serum chloride level recorded postoperatively was significantly higher in the patients with AKI. However, when the results were adjusted for covariables, the association was not significant. In the assessment of secondary outcomes, the analysis identified a significant association between AKI and arterial lactate levels on admission to the intensive care unit, but the most notable association was between AKI and the use of inotropes. Conclusions: Postoperative hyperchloraemia is common but is not independently associated with AKI. This complication is mainly related to tissue hypoperfusion or the need for postoperative inotrope use. Graphical abstract Highlights