Serum AST is one of a group of enzymes which catalyzes the interconversion of amino acids and keto acids by transfer of amino groups. Transaminases are widely distributed in body tissues with significant amounts found in the heart and liver. Lesser amounts are also found in skeletal muscles, kidneys, pancreas, spleen, lungs, and brain. Injury to these tissues result in the release of the AST enzyme to general circulation. Following a myocardial infarction, AST in serum begins to increase within 6 to 8 hours of onset of pain, reaching a peak within 18 to 24 hours and falling to normal by the fourth or fifth day.