Heparin is the drug of choice when rapid anticoagulation is required, as in prevention and treatment of venous thrombosis, pulmonary embolism, unstable angina, myocardial infarction, and vascular and cardiac surgeries. Because of its heterogenous pharmacokinetics and its side potentially severe effects, low molecular weight heparins have replaced unfractionated heparin in various medical and surgical settings. Precautions must be taken when performing central nerve block in heparinized patients.