Abstract: The present invention relates to a group of novel compounds defined as covalently bound poly-N-vinyl pyrrolidinone (PVP)-heparins. These compounds are synthesized on the basis of a novel concept that heparin molecules can be modified to have new desirable qualities by binding heparin covalently to an appropriate polymer carrier which has the desired characteristics.Heparin is hydrophilic and thereby insoluble in organic solvent. It has a short half-life in vivo. PVP-heparins, on the other hand, not only retain the anticoagulant activities of heparin, but also have the solubility (in organic solvents) and longer half-life in vivo of PVP.PVP-heparins are produced either in anhydrous or heterogeneous media wherein PVP is activated by thionyl chloride to produce an imidoyl ion which is subsequently bound to heparin. PVP-heparin produced in anhydrous media is chloroform soluble and has been found useful for coating plastics and similar substances.