• atrial fibrillation;
  • myocardial infarction;
  • valve prosthesis;
  • venous thromboembolism

Summary.  Large randomized clinical trials have clarified some issues of anticoagulation and have led to progress, such as outpatient treatment of acute deep vein thrombosis with low-molecular-weight heparin. However, many uncertainties remain and are reviewed here. When should thrombolytic therapy be used, apart from patients in shock due to pulmonary embolism? How should low-molecular-weight heparin be used in patients with extreme obesity or renal failure? The optimal duration of anticoagulation after venous thromboembolism has been the subject of many debates. With the recognition of an increasing number of risk factors for recurrence, the picture becomes increasingly complex. Lower intensity of anticoagulation with vitamin K antagonists and novel anticoagulant drugs are possible alternatives in extended secondary prophylaxis. For stroke prophylaxis in non-valvular atrial fibrillation, there is a gray zone between the groups where there is a clear indication for aspirin or for vitamin K antagonists. Anticoagulation in connection with cardioversion raises questions regarding optimal postprocedure therapy. Fine tuning of prophylaxis against thromboembolism in patients with prosthetic heart valves requires more studies of subgroups, homogenous for position and type of valve as well as presence of atrial fibrillation. The management of these patients in case of surgical procedures has not been studied properly. Secondary prophylaxis after myocardial infarction may achieve the best effect with vitamin K antagonists at an INR of 2.0–2.5 in combination with low-dose aspirin, but is it really cost-effective? Finally, many controversies exist regarding anticoagulation during pregnancy.