So heparin cofactor two is actually a molecule that enhances the activity of heparin. So let's begin by discussing what heparin actually is. So if we examine the connective tissue found surrounding our blood vessels we're going to find immune cells known as mast cells. So mast cells are these immune cells, part of our adaptive immune system which basically release an important glycos aminoglycan known as heparin. And heparin is this negatively charged glycos aminoglycan that basically enhances the activity of antithrombin three. It stimulates antithrombin three to basically form these irreversible inhibited complexes with not only thrombin but all these other factors.