Pericardial fluid reflect the composition of cardiac interstitium in myocardial ischemia. This study investigated the value of the pericardial and serum myoglobin (MG) measurements for the diagnosis of perioperative myocardial infarction (MI) after coronary artery bypass grafting (CABG). Postoperative arterial and pericardial blood samples were taken in 64 subjects undergoing elective CABG allocated to two groups according to the 12-lead electrocardiogram (ECG) abnormalities observed during the first postoperative 24 It. Group 1=normal and nonspesific ECG abnormalities, and Group 2=perioperative Q-wave MI. The occurrence of perioperative MI was associated with a dramatic increase in both serum and pericardial cardiac troponin I (CTnI) and MG concentrations. Pericardial concentrations were higher than serum concentrations during the first postoperative 24 h in all subject. However, pericardial/serum CTnI ratio in subjects in Group 2 was not statistically different from Group I at the time of admission to the intensive care unit (ICU) and did not significantly change at time intervals. On the other hand, more than two-fold increase in the pericardial/serum MG ratio was determined for all patients who experienced perioperative Q-wave MI with the lowest value as 2.75, whereas only 1 of 59 patients in group 1 had the ratio higher than 2 with the highest value as 2.15 at the time of admission to the ICU. In conclusion, determination of pericardial/serum MG ratio may be a useful tool for the early diagnosis of the perioperative MI after CABG. (C) 2004 Elsevier Ltd. All rights reserved.