The prevalence of iron deficiency in pediatric cardiac surgery patients is not very well known. Iron deficiency can lead to anemia, higher transfusion rates and possibly higher complication rates. In this retrospective study, the iron status of all patients undergoing pediatric cardiac surgery at our institution between January 2019 and december 2023 will be analyzed. Together with iron status, transfusion requirements as well as complications will be recorded. Iron status will be reported with descriptive statistics, patients with or without iron deficiency will be compared using non-parametric tests.