Prophylaxis of deep vein thrombosis (DVT) is a serious matter as the source of pulmonary thromboembolism (PTE) in hospitalized patients. Leg DVT is classified into three groups: iliac, femoral and calf types. Among them, calf type DVT is closely connected with PTE. Especially, soleal vein is the most frequent site of thrombi formation occurring with venous stagnation. Although most cases of soleal vein thrombosis are resolved soon without specific treatments: in around 20% of cases the thrombosis propagates to the proximal drainage vein as float thrombi e.g. from peroneal vein and posterior tibial vein to popliteal vein. Thereafter, the organization of thrombi leads to venous valve insufficiency, so-called postthrombotic syndrome. As a result, it worsens blood stagnation and induces recurrent thrombi formation. The broad prophylaxis of DVT in the soleal veins for inpatients is the most important point in the initial stage of hospitalization.