PURPOSE: Flow diverter stents (FDS) are used to treat aneurysms by modifying the intraaneurysmal hemodynamics and promoting a prothrombotic milieu. Thrombotic in-stent stenosis (ISS) is a common complication of endovascular treatment for intracranial aneurysms with flow diverter stents. The dominant approach to address ISS has been to either increase the dose of antiplatelet therapy agents or extend dual antiplatelet therapy (DAPT) causing ISS to resolve, while potentially exacerbating the side effects associated with DAPT. To decrease the risk of thrombotic ISS, surface coatings have been applied to flow diverter stents with promising results. METHODS: The thrombotic signature of a bare metal and a heparin coated FDS was assessed in vitro. The flow diverter stents were exposed to pulsatile blood flow in a one-pass system to assess platelet and fibrin deposition, while flow cytometry was used to assess different markers of platelet activation in blood incubated with flow diverter stents for 30, 60, and 90 minutes. RESULTS: Immunofluorescence and scanning electron microcopy results demonstrated greater fibrin and platelet deposition on bare metal flow diverter stents, while the heparin coated flow diverter stents had less fibrin and platelet deposition. A greater percentage of platelets were not only activated, but also presented higher levels of activation markers, in blood exposed to the bare metal flow diverter stents at the 90 minute time point in comparison to the heparin coated FDS. CONCLUSION: The findings demonstrate that heparin coated flow diverter stents are characterized by a lower thrombotic signature than bare metal flow diverter stents and raise the possibility of an additional therapeutic option to treat intracranial aneurysms.