Chylous effusions frequently occur after cardiac surgery due to severe damage to the lymphatic system, thus indicating that the insertion of a chest tube may be necessary. Factor XIII (FXIII) is discussed as being essential for wound healing. The aim of this retrospective study was to evaluate whether the application of a single dose of FXIII results in a reduced amount of pleural effusion, leading to an earlier release of patients from the hospital. The cases of 40 children with severe chylous effusions after open-heart surgery were examined. Twenty patients received FXIII and were compared to 20 age- and weight-matched patients who did not receive FXIII. Major parameters included the amount of effusion before and 1 and 3 days after the application of FXIII; the duration of chest tubes; the total amount of fluid loss via drainage; and the period of hospitalization. FXIII levels in plasma showed an inverse correlation with fluid loss. After application of a single dose of FXIII, a significant reduction of pleural effusion within the first 24 hours was detected. However, no difference was observed between the two groups when comparing the total amount of pleural effusions within the first 72 hours. Finally, the duration of hospitalization did not differ between the FXIII-treated and the control group. A single application of FXIII rapidly reduces the amount of chylous effusions in the early period after open-heart surgery. This effect is detectable only for 24 hours after the treatment and does not alter the further clinical outcome. Prospective clinical trials are warranted to determine if repeated application or a higher dose of FXIII may improve the clinical outcome of chylous leakages in children after open-heart surgery.