A method of manufacturing a high molecular weight heparin (HMWH) compound is disclosed. The method comprises dissolving heparin to form a heparin solution and fractionating the heparin solution via tangential flow filtration (TFF) using a membrane with a molecular weight cut off (MWCO) between about 8 kDa and about 12 kDa. The TFF yields a retentate comprising fractionated heparin with a weight average molecular weight of about 20 kDa or greater, i.e., a high molecular weight heparin compound. A substantial proportion of heparin chains in the fractionated heparin may have a high molecular weight, e.g., 50% of the heparin chains or greater may have a molecular weight of 20 kDa or greater.