BACKGROUND Atrial fibrillation (AF) is the most common arrhythmia occurring in patients after coronary artery bypass surgery (CABG). The purpose of this study was to determine whether AF characteristics were independently associated with postoperative length of stay (LOS). METHODS Two hundred ninety consecutive post-CABG patients were examined through a detailed chart review. Baseline, intraoperative, and postoperative variables and the characteristics of AF were recorded. AF episodes were divided into single episodes lasting less than 24 hours (short-lived AF) and recurrent or prolonged >or=24 hours of AF (recurrent/prolonged AF). RESULTS AF occurred in 94 (32.4%) patients. Twenty-six (27.7%) of AF patients had short-lived AF, and 68 (72.3%) of AF patients had recurrent/prolonged AF. Patients with recurrent/prolonged AF were older (P < 0.001) and more likely to have a history of prior AF (P < 0.001) relative to the other groups. Short-lived AF did not prolong LOS (7.2 +/- 2.1 days) relative to patients without AF (7.5 +/- 3.9 days), whereas recurrent/prolonged AF significantly prolonged LOS (10.4 +/- 6.1 days, P < 0.001). Multivariate analysis identified postoperative complications, recurrent/prolonged AF, age, and digoxin use as independent predictors of LOS. Recurrent/prolonged AF contributed an additional 1.1 days to LOS after adjusting for baseline clinical differences. CONCLUSIONS There are heterogenous patterns of AF after cardiac surgery. A substantial minority of AF is short-lived and isolated with no impact on LOS; however, recurrent or prolonged AF significantly affects LOS.