OBJECTIVE Atrial fibrillation (AF) is a common complication after coronary artery bypass grafting (CABG) operations, occurring in 5 to 40% of cases. A number of studies have implicated atrial ischaemia in the genesis of this arrhythmia. The aim of this study was to examine the relationship between atrial coronary anatomy and the incidence of post operative atrial fibrillation. METHODS To investigate a possible anatomical explanation to the onset of AF after CABG, 25 patients with documented AF after CABG were matched and compared to 25 patients which remained in sinus rhythm (SR). All coronary angiograms were reported blindly by a cardiac radiologist with reference to the blood supply of the sino-atrial (SA) node and atrio-ventricular (AV) node before and after surgery. RESULTS Univariate analysis of risk factors did not identify any significant difference (Fisher exact test, P > 0.05) between the two groups in age, gender, left ventricular function, ischaemic time, number of vessels diseased or grafted, renal dysfunction and withdrawal of beta-blockade. However, significant disease in the SA nodal artery was present in 2 patients of the SR group when compared to 9 in the AF group. Significant disease of AV nodal artery was present in only 4 patients of the SR group when compared to 18 in the AF group. Comparison between the two groups showed a significantly increased incidence of SA or AV nodal artery disease in the AF group, (SA: P = 0.018, AV: P = 0.0001). Mean hospital stay was 8.1 days for the SR group and 9.1 days in the AF group (P = 0.175). CONCLUSIONS Obstructive disease in the SA nodal and AV nodal arteries is more common in patients developing atrial fibrillation following coronary artery bypass surgery than those who remain in sinus rhythm. If the incidence of AF could be predicted by the anatomical distribution of arterial disease then targeting prophylaxis to this group may be possible.