Permanent and tansitory cases   Considering admission flows as laminar and permanent, the experimental study, realized using warm-film anemometry, has shown downstream from stenosis a high level of non-stationary perturbations. These perturbations have shown to be associated to very weak excitations -due to experimental material -of the upstream flow. These weak excitations, of about 1/100, can actually be representing geometric singularities of the arterial system, such as asymmetry, and can therefore be found naturally in an anatomic model. The numerical simulations realized in the condition of basic permanent and then excited flows show a good agreement with the experimental results, and put into light, for some flow rates, the existence of swirling exhausts downstream from the stenosis; these swirling exhausts being not without influence on the repartition of the parietal friction. Numerical-Experimental comparison of the speed signal downstream from stenosis, Re=315. The sensitivity of this type of flow to very weak perturbations, which can generate chaotic systems, and the non-stability amplifying character of the stenosis are the major conclusions of this study. Such effects can of course not be neglected considering their implications in real situations, and it seems clear that post-stenotic wakes are very unsteady and perturbed flows. Intuitively, this level of perturbations should be increasingly significant when asymmetries gain momentum.