Heparin (from Greek "hepar" meaning "liver" is an injectable anticoagulant.

• Highly sulfated glycosaminoglycan, having the highest negative charge density of any known biological molecule
• Usually stored within the secretory granules of mast cells, and released only into the vasculature at sites of tissue injury
• It's true physiological role in the body remains unclear, because blood anticoagulation is mostly achieved by heparan sulfate proteoglycans, derived from endothelial cells. Also, it is found in some animals that don't have a blood coagulation system → It is proposed that rather than anticoagulation, it's main purpose is defense at such sites against invading bacteria, and other foreign material
• In nature, it is a polymer of varying chain size
• Activates antithrombin III (which blocks thrombin from causing blood clotting). It is usually made from pig intestines

• Unfractionated heparin is heparin that hasn't been fractionated to sequester the fraction of molecules w/ a low molecular weight
• Low-molecular-weight heparin (LMWH) is a derivative of heparin, that has undergone fractionation to make it's pharmacodynamics more predictable. It's advantage is that it's effects are more predictable than unfractionated heparin, and doesn't require monitoring for APTT coagulation (having more predictable plasma levels), and fewer side effects. The disavantage is that the effect of the antidote protamine sulfate, results in only limited reversibility. Examples include Enoxaparin sodium (Clexane)

Source: Indystar

• Used primarily for anticoagulant
• Can be used to form an inner anticoagulant surface on various experimental and medical devices, e.g. test tubes and renal dialysis machines

• Protamine sulfate, is the antidote to heparin, is, 1mg per 100 units of heparin that had been given over the past 4 hours, to counteract the anticoagulant effect of heparin

• Warfarin
• Anticoagulant (category)