Heparin is a polysaccharide which blocks the formation of blood clots (it acts as an anticoagulant) by attaching to and interfering with the action of the protein antiprothrombin III, which plays a crucial role in clotting. Heparin is composed of D-glucosamine-2,6-disulfate and D-glucuronic acid-2-sulfate. It is used to treat thrombosis, embolisms, and related conditions.
A study done in the late 1970s indicated that heparin is useful for preventing scarring due to localized burns. To the best of my knowledge, heparin is not used for this today. However, I can vouch for its effectiveness in at least one instance, because soon after my physician father read said article in a medical journal when I was a child, I seared my leg on a heater grate. He put some heparin on me and bandanged me up, and the wound healed perfectly.
Part this writeup is based on work I did for the science dictionary at http://biotech.icmb.utexas.edu/