[PRINCIPLE]
Cardiac Troponin I (cTnI) is a cardiac muscle protein with a molecular weight of 22.5 kilodaltons. Together with troponin T (TnT) and troponin C (TnC), TnI forms a troponin complex in the heart to play a fundamental role in the transmission of intracellular calcium signal actin-myosin interaction. The human cTnI has additional amino acid residues in its N-terminal that does not exist in the skeletal forms thus making cTnI a specific cardiac marker.

Normally the level of cTnI in the blood is very low. cTnI is released into the bloodstream in forms of free cTnI and cTnI-C-T complex at 4-6 hours after myocardial cell damage. The elevated level of cTnI could be as high as 50ng/ml during 60-80 hours after AMI and remains detectable for up to 10-14 days post AMI.