A tangential regularization method for backflow stabilization in hemodynamics In computational simulations of fluid flows instabilities at the Neumann boundaries may appear during backflow regime. It is widely accepted that this is due to the incoming energy at the boundary coming from the convection term which cannot be controlled when the velocity field is unknown. We propose a stabilized formulation based on a local regularization of the fluid velocity along the tangential directions on the Neumann boundaries. The stabilization term is proportional to the amount of backflow and does not require any further assumption on the velocity profile. The perfomance of the method is assessed on a twoand three dimensional Womersley flows as well as considering a hemodynamic physiological regime in a patient specific aortic geometry.