Tissue factor pathway inhibitor (TFPI) is also known as Extrinsic pathway inhibitor (EPI), Lipoprotein - associated coagulation inhibitor (LACI), is a plasma proteinase inhibitor synthesized by vascular endothelial cells and part of it is associated with glycosaminoglycans of these cells. TFPI is a single-chain polypeptide which can reversibly inhibit Factor Xa (Xa) and Thrombin (Factor IIa) . TFPI is a secreted protein with a N­terminal acidic region, three Kunitz (K) domains separated with by two linker regions, and a C­terminal basic region. The first K domain inhibits coagulation factor VIIa complexed to tissue factor (TF) ; The second K domain inhibits factor Xa; The third K domain binds to heparin; The C­terminal basic region may have several functions. For example, it plays an important role in binding of TFPI to cell surfaces.