Heparin having a selective anticoagulant activity, procedure for making the same

Heparin fragments which possess selective anticoagulation activity and which have from 14 to 18 sugar units, with the disaccharide unit L-iduronosyl-2-O-sulphate-N-sulpho- D-glucosamine-6-O-sulphate constituting the main component, and with non-sulphated L-iduronic acid being present in a position located 3-5 sugar units from the non-reducing terminus. Pharmaceutical compositions comprising such heparin fragments. Processes for preparing the heparin fragments.