II.Unfractionated heparin (UFH)

#### **Figure 2.**

*Mechanisms of Anticoagulation. The anticoagulation system inhibits coagulation through a delicate balance between the activators and inhibitors of the coagulation cascade. At the fibrinolytic system, the balance between the activators of the fibrinolysis, including t-PA and u-PA and inhibitors, such as PAI-1 and α2-AP ensures the inhibition of fibrin formation or immediate dissolution of fibrin when it is formed. TF; tissue factor, TFPI; tissue factor pathway inhibitor, TAFI; thrombin activatable fibrinolysis inhibitor, EPCR; endothelial protein C receptor, ZPI; protein Z-dependent protease inhibitor, PZ; protein Z, TM; thrombomodulin, PC; protein C, APC; activated protein C, PS; protein S, HCII; heparin cofactor II, TM; thrombomodulin, t-PA; tissue-type plasminogen, u-PA; urokinase-type plasminogen activator, PAI-1; plasminogen activator inhibitor-1, α2-AP; α2-antiplasmin, FDP; fibrin degradation products. The dashed arrows indicate inhibition while thick arrow lines indicate activation.*

## *Anticoagulants and Hypercoagulability DOI: http://dx.doi.org/10.5772/intechopen.103774*

Heparin forms a complex with antithrombin III (ATIII) and inactivates several coagulation factors, including FVII. It has a rapid onset of action and a short halflife. Heparin is monitored by activated partial thromboplastin time (aPTT) and anti-Factor Xa activity. The ratio of 1.5–2.2 times is the recommended target for aPTT [12].
