Markers of cardiac myocyte injury have contributed over the years to the diagnosis and to the assessment of size of myocardial infarction. Recent evidence suggests that measurement of the release of cardiac contractile proteins into the bloodstream at lower levels may be useful in the clinical assessment of patients who have acute or chronic heart failure. The advent of a new generation of high-sensitivity immunoassays for cardiac troponins offers challenges for scientists and clinicians and will likely change the understanding and interpretation of cardiac injury.