Veins have valves that keep blood moving back toward the heart. Problems occur when a valve no longer works properly. This allows blood to flow backward in the vein, creating pressure on the valves below.
Swollen ankles, tired aching legs
Pooling. When a poorly closing valve allows blood to flow backwards, blood can back up and collect, or pool, in the veins. Pooling of blood causes swelling, especially near the ankles and feet.
Varicose veins. When a valve is damaged, the backup of blood results in higher pressure in the veins below. This high pressure may strain the wall of the veins, causing them to enlarge. Varicose veins are enlarged superficial veins that become visible bulges under the skin.