Aspartate aminotransferase (AST) is an enzyme found in the liver, heart, muscles, and other tissues. It is released into the bloodstream when cells are damaged, making it a useful marker for assessing liver injury and other tissue damage. Elevated AST levels are often seen in liver conditions such as hepatitis or fatty liver disease but can also reflect muscle injury or heart disease. AST is typically interpreted together with alanine aminotransferase (ALT) to better evaluate the type and extent of liver damage.