['Previous studies have demonstrated that microRNA-21 (miR-21) is involved in the pathogenesis of myocardium infarction and cardiac fibrosis; the present study aimed to investigate its potential role in the diagnosis of acute myocardium infarction (AMI).', 'A cohort of patients with AMI and angina pectoris (AP) were studied, plasma miR-21 level was determined by Realtime-PCR.', 'We found that the plasma miR-21 level was significantly elevated in patients with AMI compared with those with AP or healthy people. Further studies demonstrated the correlation of miR-21 and several traditional markers such as creatine kinase (CK), creatine kinase-MB (CK-MB) and troponin I (cTnI) in study subjects. Finally, receiver-operator characteristic curve (ROC) analysis showed that miR-21 has similar diagnostic ability compared with CK, CK-MB and cTnI.'] Is plasma microRNA-21 a potential diagnostic biomarker of acute myocardial infarction?