This patent document relates to antibodies, antigen-binding antibody fragments (Fabs), and other protein scaffolds, directed against human antithrombin β complexed with heparin and/or heparin-like structure (ATβH). These ATβH binding proteins can block the anti-coagulant activity of ATβ to induce coagulation. Therapeutic uses of these antibodies and binders are described herein as are methods of panning and screening specific antibodies.