Veins have valves, which when functioning properly, keep the flow of venous blood moving from the feet toward the heart against gravity. When these valves leak, blood flows in the wrong direction causing it to pool in the veins of the leg. This pooling of blood results in increased vein pressure and volume, causing the veins to get wider and longer leading to visible varicose veins. Significant bulging varicose veins are usually due to veins below the skin surface, most often this underlying vein is the saphenous vein. The saphenous vein is not visible without the aid of an ultrasound. The stretching of the vein walls that occurs with this process is responsible for the symptoms that most patients have.