Device for avoiding deep vein thrombosis in the leg veins, comprising at least one closed system with two chambers communicating with each other and filled with a fluid medium surrounded by a flexible covering, namely one compression chamber located underneath a foot sole and one expansion chamber which has a smaller volume than the compression chamber in a condition free from external forces and in case of internal pressure equalization between the two chambers (5, 6), wherein a) In use, the compression chamber is located entirely underneath the heel; b) the expansion chamber has a longitudinal shape with an approximately elliptic perimeter, and is located between the inner ankle and the achilles tendon, in close contact with a local perforating vein system so that, when the compression chamber arranged on the foot sole is compressed, the blood is pressed by the in that case expanded expansion chamber from a local perforating vein into a deeper vein; c) in use, a tubular connecting element connecting the compression chamber and the expansion chamber extends along the inner side of the foot; d) the device comprises a retaining band which is flexible, but not elastic or hard to expand, and which encloses the expansion chamber from outside and by which the foot ankle can be enclosed in such that e) the expansion chamber which is expanding after being filled from the compression chamber cannot evade outwardly, but that the expansion of the expansion chamber is transferred to the perforation vein underneath the expansion chamber thereby compressing it and discharging it, and wherein f) the calf is not covered by the device, g) further wherein the compression chamber, the expansion chamber as well as the tubular connecting element are formed by two congruent cuttings of a medically tolerable material which are put on each other, and which are completely welded in a close manner along their entire perimeter, h) and finally wherein a free side section of the compression chamber is connected to the retaining band via a short connecting band. a) In use, the compression chamber is located entirely underneath the heel; b) the expansion chamber has a longitudinal shape with an approximately elliptic perimeter, and is located between the inner ankle and the achilles tendon, in close contact with a local perforating vein system so that, when the compression chamber arranged on the foot sole is compressed, the blood is pressed by the in that case expanded expansion chamber from a local perforating vein into a deeper vein; c) in use, a tubular connecting element connecting the compression chamber and the expansion chamber extends along the inner side of the foot; d) the device comprises a retaining band which is flexible, but not elastic or hard to expand, and which encloses the expansion chamber from outside and by which the foot ankle can be enclosed in such that e) the expansion chamber which is expanding after being filled from the compression chamber cannot evade outwardly, but that the expansion of the expansion chamber is transferred to the perforation vein underneath the expansion chamber thereby compressing it and discharging it, and wherein f) the calf is not covered by the device, g) further wherein the compression chamber, the expansion chamber as well as the tubular connecting element are formed by two congruent cuttings of a medically tolerable material which are put on each other, and which are completely welded in a close manner along their entire perimeter, h) and finally wherein a free side section of the compression chamber is connected to the retaining band via a short connecting band.