Chronic venous insufficiency (CVI) describes a condition affecting the veins in the lower extremities (legs) with venous hypertension. This leads to pain, swelling, edema, skin changes, and ulcerations in the legs.

Chronic venous insufficiency is also called "venous reflux". Venous reflux occurs when venous valves don't function adequately, leading to reversal of blood flow through the valves during standing or sitting. Venous reflux most commonly occurs when vein valves weaken due to genetic influences or multiple pregnancies, among other factors.

When the valves in the veins of the lower body do not properly channel blood flow back to the heart because of blockage or venous valve malfunction, blood flow slows, pressure increases, and swelling occurs in the legs and feet. Venous reflux is often self-perpetuating, as the pooling of blood in veins distends them, which pulls apart the valve leaflets of the next, lower valve and causes reflux farther down the leg.

As blood pools in lower extremities, veins further swell, leading to pain, pigmentation of the skin, and clots in the varicose veins (phlebitis).