In the paper, the LES results of a flow by using a model of the blood vessel with a one-side 70% stenosis, at a Reynolds number of 1803, have been presented. The Germano – Lilly model was applied to subgrid viscosity evaluation. A jet-like zone and a recirculation one were found to stand out just behind the stenosis, and a pair of secondary-flow vortices forms being within each of them. Instabilities of the mixing layer initiated the flow turbulence with formation of vortex structures of different scales at the boundary between the reverse flow zone and the jet. These structures filled the whole cross-section of the vessel about the flow attachment point. Turbulent shear stresses were significant in magnitude only at a flow section of about four-caliber length. Further downstream, the flow relaminarised.