An optimized, second-generation, PEGylated aptamer with antithrombotic property. ULvWF multimer-targeting agent ARC1779 blocks the binding of von Willebrand factor (vWF), via the A1 domain, and ultra-large vWF multimers to platelets, as well as interfering with the binding of platelet receptor glycoprotein Ib, thus reducing platelet adhesion, aggregation and thrombus growth in arterial beds. Unlike other antiplatelet agents, this aptamer can be readily reversed by binding to a complementary sequence of oligonucleotides, and may therefore offer potential therapeutic benefit in surgery.