Atrial fibrillation (AF) is a common complication after coronary artery bypass grafting. Atrial remodeling has been observed in AF and has been associated with the development of this arrhythmia. Because 3-hydroxy-3-methylglutaryl coenzyme A inhibitors (statins) have been demonstrated to modify remodeling, we hypothesized a protective role of statins against postoperative AF. We also hypothesized that extracellular matrix turnover and brain natriuretic peptide (BNP) might be related to such atrial remodeling. We studied 234 consecutive patients who underwent coronary artery bypass grafting (173 men; 65 ± 9 years of age) in whom the occurrence of postoperative AF was monitored. In a subgroup of 66 patients, we measured plasma levels of matrix metalloproteinase-1 (MMP-1), its inhibitor, tissue inhibitor matrix metalloproteinase-1 (TIMP-1; as indexes of extracellular matrix remodeling), and N-terminus pro-BNP (related to left ventricular function) at baseline and at 24 hours after surgery. Of 234 patients, 66 (28.2%) developed postoperative AF. In multivariate analysis, previous AF was related to an increase in the development of AF (odds ratio 11.92, 95% confidence interval 2.37 to 59.98, p = 0.026), whereas statin use was related to a decrease in arrhythmia (odds ratio 0.52, 95% confidence interval 0.28 to 0.96, p = 0.038). A higher TIMP-1/MMP-1 ratio at 24 hours after surgery was present in those who did not develop postoperative AF (p = 0.043). Statin use was associated with increased TIMP-1 levels and TIMP-1/MMP-1 ratio (p = 0.027 and 0.036, respectively). No significant relations to N-terminus pro-BNP were seen. In conclusion, previous AF and nonuse of statins are significantly associated with AF after coronary artery bypass grafting. Statin use may be protective against AF after coronary artery bypass grafting, possibly due to alterations in the extracellular matrix and remodeling after coronary artery bypass grafting.