CARDIAC CLINICS NEAR ME Troponin The enzymes troponin I and troponin T are normal proteins that are important in the contractile apparatus of the cardiac myocyte. The proteins are released into the circulation between 3 and 4 hours after myocardial infarction and remain detectable for 10 days following. This long half-life allows for the late diagnosis of MI but makes it difficult to detect re-infarction, as can occur in acute stent thrombosis after percutaneous coronary intervention. There are a number causes for troponin elevation not related to myocardial infarction; however, troponin elevation is much more sensitive than myoglobin and even creatine kinase.