Some people with deep vein thrombosis will not notice any symptoms, but this condition can cause swelling of the feet and ankles, leg cramps, and foot or ankle pain. When a blood clot forms in a leg vein, it disrupts blood flow, causing swelling and discomfort. Blood clots on the legs can cause swelling of the ankles and feet. Then the blood starts to accumulate in the legs instead of circulating well, which can cause swelling, and peripheral vascular disease (PVD) is the leading cause. A blockage in the lymphatic system can cause the tissues to swell with fluid. The condition can cause shortness of breath and severe chronic swelling of the legs and ankles.