Interactive model illustrates a blood circulation and thrombus formation in injured vessels of various sizes. An availability of injury and a kind of vessel may be selected by any of two radio-buttons in bottom part of the window. Animation is initiated by clicking on the "Start" button. The view of vessel is essentially enlarged. Bleeding is a dangerous state, sometimes it may be hazardous to life. The blood flows out through the vessel hole. There are special mechanisms aimed to arrest the bleeding in an organism. Platelets adhere to the place of failure at once after damage and so-called primary platelet plug is formed. This mechanism is able to arrest bleeding in small vessels. In large vessels (intensive blood flow, high blood pressure) this mechanism is not able to arrest bleeding, in this case blood coagulation is additionally involved in hemostasia. After activation of some components of blood plasma the fibers of protein fibrin are formed there. This fibers sustain the initially arisen primary platelet plug. The thrombus is formed. Other blood cells - leucocytes, erythrocytes - may be included in the fibrinous net and stay there. Afterwards thrombus is compressed, condensed (grume retraction). Simultaneously, platelets release compounds that induce an endothelial cell proliferation and the vessel regeneration. Concurrently, thrombus must be gradually dissolved to do not impede blood circulation. Disturbance of these complicated processes may cause two kinds of diseases. If thrombus either does not arise or may be just poorly formed then it leads to hemorrhagic diathesis (bleeding sickness). On the other way, thrombus either may be too large or may arise when there is no need in it - in such case it can plug up the vessel and therefore blood supply of tissue would be disturbed. This may result in, for example, myocardial infarction. In serious wounds the large arteries and veins may stay open for a long time and finally, in an absence of medical assistance, may result in a loss of blood and lead to a death of the organism. Then, to arrest bleeding a set of various medical facilities are applied, like fascias, gauze bandage, garrots). The animation is operated by the "Stop" and "Reset" buttons.