Objectives: To examine, using cardiac magnetic resonance (CMR), the utility of cardiac biomarkers for the determination of myocyte necrosis and function after coronary artery bypass grafting (CABG), and to test the recently updated guidelines for the diagnosis of postoperative myocardial infarction (type V MI). Methods and results: Forty patients included in a single-centre randomised trial of two surgical techniques for performing CABG underwent serial assessment with CMR biochemical markers. Cine and delayed enhancement CMR (DE-CMR) for assessment of left ventricular (LV) function and irreversible myocyte necrosis was performed and levels of troponin I (TnI) and creatine kinase-MB isoform (CK-MB) were determined. The area under the curve for TnI strongly correlated with the mass of new myocyte necrosis as assessed by DE-CMR (r=0.83, p<0.001), compared with CK-MB (r=0.39, p=0.06). Furthermore, routine assessment of TnI alone at 24 h (>6.6 μg/l) predicted type V MI on DE-CMR with a sensitivity of 88% and specificity of 97%, whereas CK-MB predicted type V MI with a sensitivity of 75% and specificity of 87%. Conclusions: Biomarkers alone (TnI), at an appropriate threshold appear robust for the detection of type V MI, independently of supplementary evidence, as suggested by the ESC/ACCF/AHA/WHF criteria.