Atrial fibrillation (AF) may occur during or after percutaneous coronary interventions (PCI). The purpose of the study was to determine the clinical, angiographic and electrophysiological predictors of AF after PCI. 225 patients undergoing PCI (mean age of 65 ± 11 years) who had sinus rhythm (SR) before balloon inflation were taken to study. Of these 22 developed AF in catheterization laboratory after balloon inflation or in 24 h following PCI (AF group), 203 did not (SR group). The patients in AF group were older (67 ± 9 vs. 63 ± 8 years, p < 0.05) and their ventricular ejection fraction was lower than SR group (56 ± 5 vs. 45 ± 7%, p < 0.05). The P-wave dispersion was significantly higher in AF group than SR group (53 ± 8 vs. 29 ± 10 ms, p < 0.001). For the patients with ST elevation myocardial infarction, the time from the onset of symptoms to balloon inflation was 3.7 ± 1.7 h in SR group. It was longer in AF group (4.1 ± 1.8 h, p < 0.05). TIMI perfusion grades 2 and 3 were achieved in 23 of 27 patients in SR group, and 5 of 8 patients in AF group. Multivessel disease was documented in 93 of the patients in SR group, and 12 in AF group. Clinical reperfusion was thought to be established in 20 in SR group, and 4 in AF group. In conclusion, our results show the importance of clinical factors, angiographic results and P-wave analysis in prediction of AF following PCI.