Abstract Background and introduction Information about optimal use of heparin in flush fluids during endovascular thrombectomy (EVT) for acute ischemic stroke (AIS) is lacking. Variables that determine total heparin dose entering the patient by flush fluids are mostly unknown. We aim to provide insight in these unknown but highly relevant variables. Methods and results We performed a survey including all Dutch interventionists performing EVT (n = 79) collecting data on used concentration of heparin in infusion bags, number of infusion bags connected, timing of connecting the flush line and the dripping rate (ml/sec). We calculated potential heparin dose entering the patient per hour through flush fluids (IU/h). Twenty-eight interventionists (35%) representing 17 Dutch stroke centers completed the survey. Eight interventionists responded not to add any heparin to flush fluids (18%). The highest amount of heparin entering the patients was 13,500 IU/h, reported by 2 interventionists from the same center (4%). Conclusions We provide insight in the use of heparinized flush during EVT in the Netherlands. Total amounts of heparin administered via flush fluids may go up to 13,500 IU/h. With this paper we intend to set a starting for future research and development of guidelines on the use of heparinized flush fluids during EVT for AIS.