An antithrombin is a small molecule which inactivates several enzymes of the coagulation system.

stopsbloodblclots from forming

Antithrombin

Gunnar Pejler has written:

'Why does Heparin bind antithrombin?' -- subject(s): Heparin

Heparin, the natural anticoagulant contained in basophil and mast cell granules. It inhibits thrombin by enhancing the activity of antithrombin III. Heparin also inhibits the intrinsic pathway.

antithrombin III and protein c inhibit the activity of other intrinsic pathway procoagulants.