Atrial fibrillation (AF) remains a frequent complication after coronary artery bypass graft surgery (CABG). We evaluate the association of AF occurrence and serum cardiac troponin I (cTnI) levels in the early postoperative period after CABG. Between April 2009 and January 2010, 95 consecutive patients with sinus rhythm who underwent CABG were evaluated. The patients were divided into two groups according to their postoperative rhythms: sinus rhythm group (SR) and AF group (AF). Demographic, clinical variables, and troponin I were evaluated at the pre- and postoperative times. There were no clinical or demographic differences between the two groups. The postoperative troponin I in the SR group was lower than that in the AF group (0.66 +/- 1.62 vs. 2.07 +/- 5.01 ng/ml; P = 0.029). Using the receiver operating characteristic curves was found as the best cut-off value to predict AF occurrence at the value of 0.901 ng/ml. Using this value of cTnI, a sensitivity of 60% and a specificity of 87% for AF onset prediction were observed. The cTnI serum levels at the postoperative period after CABG were higher in patients who subsequently developed AF. The cut-off value of 0.901 ng/ml is useful for prediction and preventive therapeutic actions.1412225