Pathophysiology Over 150 years ago Virchow recognised three prerequisites for thrombogenesis: abnormal blood flow, vessel wall abnormalities, and blood constituent abnormalities. This concept has been extended by modern knowledge of the endothelial function, flow characteristics, and blood constituents including haemorheological factors, clotting factors, and platelet physiology. As thrombus consists of platelets and fibrin (and often bystanding erythrocytes) optimum antithrombotic prophylactic therapy can and should be directed towards both.