There are many reasons swelling can occur on the lower legs. But one of the signs of venous insufficiency is swelling around the ankles and calves. Healthy veins pump blood upward through muscle contractions in the lower limbs. These elastic veins have tiny valves that maintain proper blood flow by keeping blood flowing in only one direction: back up to the heart. Venous insufficiency occurs when the valves in veins don’t properly close Instead, the blood pools or refluxes in the vein. This can lead to extravasation of fluid, creating the swelling of veins you may be experiencing.