WASHINGTON, DC - JANUARY 20: U.S. President Donald Trump delivers his inaugural address on the West Front of the U.S. Capitol on January 20, 2017 in Washington, DC. In today's inauguration ceremony Donald J. Trump becomes the 45th president of the United States.
One-Way Valves in the Veins. One-way valves consist of two flaps (cusps or leaflets) with edges that meet. These valves help veins return blood to the heart. As blood moves toward the heart, it pushes the cusps open like a pair of one-way swinging doors (shown on the left).
In some instances, the absence or weakness of valves in the veins may cause poor venous circulation (blood flow in the veins) and lead to varicose veins. Valves inside veins normally act to ensure that blood in the veins does not flow in a backward direction (retrograde) away from the large (deep) veins and the heart.