TNNI3 and myocardial infarction: The Fourth Universal Definition of Myocardial Infarction [8] is based on the clinical distinction between two different clinical conditions: (a) acute myocardial injury, characterized by significant changes over time in the hs-cTnI and hs-cTnT levels in a patient, and (b) chronic myocardial injury (i.e., heart damage), characterized by nearly stable biomarker levels.