UFH predominantly acts by binding to and increasing the natural anticoagulant activity of Antithrombin (AT) and Tissue Factor Pathway Inhibitor (TFPI). A number of in vitro and in vivo studies have demonstrated clear differences in the AT-dependent activity of UFH in children comparedwith adults. However, there are no studies to date, directly observing UFH-dependent TFPI release in children receiving UFH via a continuous intravenous (IV) infusion. The results of our study are in accordancewith studies conducted in adults which suggest that TFPI significantly contributes to the inhibition of thrombin generation by UFH in the haemostatic system of children. However future studies are required to further investigate these findings.