Myocardial infarction has long been a subject of research in cardiology and biochemistry. Within the past few years, a number of new phrases, micro-infarction, minor cardiac damage and non-ischemic cardiac damage have been frequently used and discussed since cardiac troponin I (cTnI) was introduced. Using this sensitive and specific biomarker it is now possible to detect minor cardiac damage occurring in different clinical settings: spontaneous, trauma, thermal injury, septic shock, or during cardiovascular surgery. The advent of this marker also opens a subject on the pathophysiologic aspect of non-ischemic cardiac damage that has not yet been fully understood and verified. This article reviews current knowledge of cTnI and its relationship with unstable angina and non-ischemic cardiac damage. The clinical implication of recent research findings on cTnI is also discussed.