Study objectives: Perioperative myocardial infarction (PMI) during coronary artery bypass grafting (CABG) is an important clinical problem because it is closely associated with increased morbidity and mortality. The diagnosis of PMI is, however, associated with several problems. Due to the surgical trauma, the usual indicators of myocardial infarction (pain, ECG changes, and elevated biochemical markers of infarction) have uncertain diagnostic value. The primary aim of this study was to illustrate the levels of the biochemical markers after uncomplicated bypass surgery defined as no clinical or ECG evidence of PMI, and no graft occlusion at 7 days by repeat angiography; and secondarily, to establish biochemical diagnostic discrimination limits for detection of in-hospital graft occlusion. Methods and results: One hundred three patients undergoing elective CABG were closely monitored by serial measurements of creatine kinase (CK)-MB mass, myoglobin, troponin T, and troponin I, and underwent a repeat angiography before discharge. Seven patients had ECG evidence of PMI. Peak troponin T and CK-MB values were significantly higher in these seven patients, although the diagnostic performances of the optimally chosen cutoff levels for diagnosing AMI were fair. Twelve patients had at least one occluded graft shown by repeat angiography. Peak values of CK-MB and troponin T were significantly higher in patients with graft occlusion (52.2 μg/L vs 24.7 μg/L, p 3 0.01; and 3.7 μg/L vs 1.0 μg/L, p 3 0.05, respectively). By multivariate analysis, a diagnostic discrimination level of 30 μg/L for CK-MB did not reach statistical significance; however, the independent diagnostic value of a cutoff level for troponin T at 3 μg/L reached a level of significance (p 3 0.06). Discussion: We have suggested normal values of four different biochemical markers of infarction after uncomplicated coronary bypass surgery. Patients with in-hospital graft occlusion had higher peak CK-MB and troponin T values. However, the overlap with patients without graft occlusion is substantial, and the patency status in the individual cannot be reliably predicted from these noninvasive tests.