Cardiac Troponin-I (cTnI) is a 23.8 kD regulatory subunit of the troponin complex that is associated with the actin thin filament within cardiac muscle cells. The troponin complex is composed of troponin-C and troponin-T, and it plays an integral role in the regulation of cardiac muscle contraction. Extensive clinical studies have demonstrated that cTnI is slowly released into the blood within hours of myocardial infarction (MI) or ischemic damage. cTnI elevation is detectable in serum within 4-6 hours after the onset of chest pain, and can remain elevated for up to 10 days following MI. cTnI measurements are highly specific for myocardial damage, and can be useful for identifying cardiac injury from different sources, including surgery, trauma, and intensive exercise. Clinical studies have also shown the patients with acute coronary syndromes (ACS) were at greater risk of progressing to MI if cTnI is elevated relative to an upper reference limit for healthy individuals. This has spurred increasing attention in recent years on high sensitivity cTnI measurement. Potential benefits include more rapid diagnosis in ACS, population screening, prognostic information in stable patients, and clinical drug development.