Heparin is a highly sulphated glycosaminoglycan discovered about 90 years ago, and since then is widely used in medicine as an anticoagulant drug, administered for parenteral, intravenous and subcutaneous. Antithrombin (AT) is a small protein molecule that inactivates several enzymes of the coagulation system. This book discusses the clinical applications of heparin; new antithrombotic and anti-platelet drugs that can be used instead of heparin; and heparin's effect on vascular health.