Introduction: Aim of this study was to investigate the release kinetics of three different marker proteins of myocardial ischaemia (Myoglobin, Troponin T and Myosin) following aortocoronary bypass surgery and elucidate their value in the diagnosis of perioperative myocardial infarction. methods: After institutional approval and informed consent 26 patients scheduled for aortocoronary bypass surgery were investigated. 4 patients (group 1) suffered perioperative myocardial infarction (electocardiographic findings together with elavated CK MB activity measurements for more than 18 hours), 4 patients (group 2) minor perioperative myocardial ischaemia (elevated CK MB measurements for more than 4 but less than 18 hours with or without ST-T segment changes). 18 patients (group 3) had uneventful surgery (CK MB activity measurements ~20 U/I only withhin 4 hours of aortic declamping). CKMB activity, Myoglobin, Troponin T and Myosin were measured before surgery, before cardiopulmonary bypass, after aortic declamping, 1, 2, 3, 4, 8, 12, 16 and 20 hours later and daily thereafter for 7 days. results: Myoglobin concentrations peaked 1 hour after aortic declamping (group 1: mean 949, SD 343 ug/l; group 2: mean 361, SD 97 ug/l, group 3: mean 313, SD 36 ug/l) and again 12 to 24 hours later (group 1: mean 3303, SD 2536 ug/l, group 2: mean 322, SD 109 ug/l, group 3: mean 255, SD 51 ug/l). Peak concentrations differed significantly between patients with perioperative myocardial infarction (group 1) and group 2 (pc 0.05) and group 3 (pe 0.05) patients. Peak concentrations did not differ significantly between patients with minor perioperative myocardial ischaemia (group 2) and group 3 patients. Myoglobin concentrations in general returned to preoperative values withhin 24 hours. In all three groups Troponin T measurements were elevated after aortic declamping, reached peak values withhin 24 hours and stayed that high for 7 days (peak values: group 1: mean 33.7, SD 20.1 ug/l, group 2: mean 2.9, SD 0.9 ug/l, group 3: mean 1.43, SD 0.20 ug/l). Troponin T measurements differed significantly between all three groups (p 21 ug/l for more than 24 hours) and electrocardiographic findings suggestive for myocardial ischaemia (1 patient) or postoperative tachyarrhythmias (2 patients). Myosin measurements did not exceed 300 ug/l before postoperative day 4 (group 1) or postoperative day 5 (group 2 and 3). Myosin measurements remained elevated until postoperative day 7. Myosin measurements did not differ significantly between the three groups. discussian; Myoglobin measurements enable very early diagnosis of perioperative myocardial infarction (1). Myoglobin measurements are only useful in the diagnosis of extended myocardial necrosis and are in general elevated for no more than 24 hours. Troponin T measurements enable early diagnosis of perioperative myocardial necrosis and detect small myocardial infarction as well. Troponin T concentrations stay high in patients with perioperative myocardial infarction for at least one week. Troponin T measurements detect small myocardial necrosis unrecognized by CK MB activity measurements. Myosin measurements do not enable diagnosis of perioperative myocardial infarction before postoperative day four.