Pooling of venous blood in the legs that causes swelling, varicose veins and ulcers. When the calf muscles contract they squeeze blood through the leg veins back toward the heart. Normally these leg veins contain valves that allow the blood to travel upward but prevent backward flow. In chronic venous stasis (CVI) the veins do not work properly, allowing the blood to pool in the legs. This causes the symptoms. The following conditions are associated with this disorder: blood clots (deep venous thrombosis / DVT), obesity, jobs or hobbies that require frequent and prolonged standing, being female, smoking, family history of CVI, advanced age, previous broken leg or other severe trauma, and pregnancy.