Alanine aminotransferase (ALT) measurements are useful in the diagnosis and treatment of heart disease and certain liver diseases, eg., viral hepatitis and cirrhosis. ALT activity in tissue is generally much lower then aspirate aminotransferase (AST) activity and is found in highest concentrations in 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.