For study of the microcirculation various in vitro and in vivo techniques exist. Whereas in vivo systems impress with their physiologic fidelity, in vitro systems excel with the amount of reduction that can be achieved. Here we introduce the auto-perfused ex vivo flow chamber, designed to study murine leukocytes and platelets under well defined hemodynamic conditions. In our model, the murine heart continuously drives the blood flow through the chamber providing a wide range of physiologic shear rates. We used a balance-of-force approach to quantify the prevailing forces at the chamber walls. Numerical simulations show the flow characteristics in the chamber based on a shear-thinning fluid model. We demonstrate specific rolling of wild type leukocytes on immobilized P-selectin, abolished by a blocking mAb. When uncoated, the surfaces having a constant shear rate supported individual platelet rolling, whereas on areas showing a rapid drop in shear platelets interacted in previously unreported grape-like conglomerates, suggesting an influence of shear rate on the type of platelet interaction. In summary, the ex vivo chamber amounts to an external vessel connecting the arterial and the venous systems of a live mouse. This method combines the strengths of existing in vivo and in vitro systems in the study of leukocyte and platelet function.