She has a history of periodic chest pain for which she uses nitroglycerine sublingually, but today her medication did not relieve

the pain. Her blood pressure is 140/100 mm Hg, pulse — 130/min., respiratory rate — 18/min., temperature — 37°C. A bedside

electrocardiogram shows ST-segment elevation in leads II, III, and aVF. Blood is drawn and sent to the lab, which is positive

for specific biomarker. A diagnosis of acute inferior myocardial infarction is made, and the patient is sent to the catheterization

lab for angioplasty with stent placement. Which of the following is the most likely specific and sensitive biomarker of cardiac injury?