Recent studies show an important influence of gender on inflammatory reactions. Cardiac surgery is associated with a major systemic inflammatory response. The investigators want to evaluate the gender influence on morbi-mortality in pediatric cardiac surgery patients.

Gender plays an important role in the inflammatory response. This is due to hormonal influences, but also different genetic regulation of pro-inflammatory cytokines, as nuclear facto kapp B. it is also know that cardiac surgery, especially under cardiopulmonary bypass, is associated with a major inflammatory response. This response is even more marked in pediatric cardiac surgery. The investigators hypothesise that there is a gender influence on mortality and major morbidity in paediatric patients undergoing cardiac surgery. The investigators will do a retrospective cohort study, analysing the local database of all paediatric cardiac surgery cases from jan 2006 to dec 2019. Primary outcome will be any difference in mortality and /or major morbidity according to gender.

Statistical analysis:

The investigators will use a propensity score on 11 pre-operative variables clinically judged relevant. Both group will be matched until a absolute standardised difference < 15% is obtained. This type of matching, contrary to a P value, is independent of sample size. Variables will be presented as mean, standard deviation or percentage for frequency distributions. After propensity score matching, logistic regressions will be performed on binary variables and linear regressions on continuous variables. A Bonferroni correction will be used for multiple comparisons.

Inclusion Criteria:

• All patients undergoing paediatric cardiac surgery with cardiopulmonary bypass

Exclusion Criteria:

• Jehova's witness

All patients undergoing paediatric cardiac surgery with cardiopulmonary bypas at our institution from jan 2006 to dec 2019.