Alanine Aminotransferase (ALT) measurements are particularly useful in the diagnosis and management of certain liver diseases, e.g., viral hepatitis and cirrhosis. ALT activity in tissue is generally much lower than aspartate aminotransferase (AST) activity and is found in highest concentrations in the liver. Significant elevations of ALT occur only in diseases of the liver. ALT is often measured in conjunction with AST to determine whether the source of the AST is the liver or the heart. ALT is normally not elevated in cases of myocardial infarction, i.e., a normal ALT, in conjunction with an elevated AST, tends to suggest cardiac disease. However, slight elevations of ALT may occur if an infarct destroys a very large volume of heart muscle.