Aspartate Aminotransferase (AST) Test - This test measures the level of AST enzyme in the blood, which is found in high amounts in the heart and liver, and to a lesser extent in muscles and other organs. Damage to these organs can release AST into the bloodstream. It's particularly useful for detecting heart damage (like after a heart attack) and liver diseases such as hepatitis, liver necrosis, cirrhosis, and liver cancer.