The investigators would like to investigate the contribution of the contact activation system to the formation of thrombi. The formation of a thrombus within the vascular bed is the main cause for occlusion of an artery or vein, which can lead to an infarct such as a heart attack. Due to the other functions of the contact system it is important to fully understand how the contact system contributes to thrombus formation, before it can be used as a target in the treatment of arterial thrombosis. The aim of this study is to determine the contribution of the proteins of the contact system, mainly FXII and FXI, in the platelet mediated formation and degradation of thrombi. This will be studied in flow models (perfusion-flow model and Chandler loop), in a static model (ROTEM®) and using thrombin generation assay.