The venous system has internal valves that prevent backflow of blood. The elastic layer and thin smooth muscle wall allow the veins to expand in volume without tearing. For a number of reasons, the outflow of blood can be impaired, which leads to congestion. This condition is called venous stasis or venous congestion . Localization of the pathological process is observed in those areas where there are vascular accumulations: lower extremities, pelvis, lungs and head. The onset of the disease is associated with an increase in blood viscosity and excessive elasticity of the damaged vein. Outwardly, the disease manifests itself in the form of protruding veins, the formation of spider veins and muscle weakness.