The main possibility that the feet will swell after sitting for a long time is the presence of venous valve insufficiency in the lower limbs. This disease causes the structural valves within the veins, which are equivalent to small valves that open in one direction, to lose their function, so that during the return flow of blood from the feet to the heart, there is a partial regurgitation, causing an increase in pressure within the veins of the lower extremities, leading to the accumulation of fluid in the veins in the tissue spaces and causing edema. And because the role of muscle pump is significantly weakened when sitting, it cannot assist the venous return to the heart, so it leads to edema in the feet, once this situation occurs, the lower limb venous valve function examination should be performed as soon as possible to clarify the diagnosis and treat accordingly.