The present review provides a review of haemostasis and thrombosis. It describes the basic mechanisms of the blood's coagulable states, as well as their associated bleeding and thromboembolic disorders. Endothelial cells present a nonthrombogenic surface. In contrast, after contact of blood with a synthetic surface (e.g. mechanical heart valves) local thrombus formation and embolism can occur. Anticoagulant therapy is required to prevent these complications in patients with artificial implants.