Troponin. Considered a cardiac "enzyme." Troponin is an integral part of the myocardium (and every other muscle), and after a myocardial infarction has occurred troponin is released because of damage to the muscle. Troponins I and T (specific to myocardium) are choice markers for detecting MIs and considered to be diagnostic. However, their levels remain elevated and make detection of a reinfarction difficult.