Merck Manual

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Valves in Varicose Veins
Valves in Varicose Veins
Valves in Varicose Veins

In a normal vein, the cusps of the valves close to prevent backward flow of blood. In a varicose vein, the cusps cannot close because the vein is abnormally widened. Consequently, blood can flow in the wrong direction.

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Varicose Veins