and the fast skeletal (TNNI2). Because the heart uses its own version, blood levels of cTnI is used as a clinical marker.
* Mammals have three troponin T (TnT) genes: the cardiac (TNNT2, cTnT), the slow skeletal (TNNT1), and the fast skeletal (TNNT3). Again, because the heart uses its own version, cTnT is used as a clinical marker.

In addition to the myocardium, there are reports of CTnI and CTnT expression