Unfractionated heparin (UFH, commonly called heparin) is an indirect anticoagulant commonly administered prophylactically to inpatients at risk of thrombosis. Anticoagulants, including UFH, are considered high alert medications when used for treatment. As such, assays monitoring levels of UFH are extremely important to avoid adverse effects for patients. This activity will provide improved understanding for clinicians and laboratorians related to the monitoring of UFH and related forms of heparin. Emphasis will be placed on the role of the chromogenic anti-Xa assay as a measure of heparin activity along with clinical scenarios and outcomes studies.