To answer whether atrial ischemia plays an important role in the genesis of atrial fibrillation in patients with coronary artery disease, we analyzed the electrocardiograms obtained at the time of coronary angiography and left ventriculography in 3220 consecutive patients. Atrial fibrillation was found in 74 (2.3%). Among those with significant coronary artery disease were 49 (66.2%) patients with atrial fibrillation and 88.5% with sinus rhythm (P<0.02). Angiograms of patients with atrial fibrillation and significant (>50%) coronary stenosis were re-evaluated and results compared to the control group which consisted of 108 consecutive patients who were in sinus rhythm at the time of coronary angiography. There were no differences between groups with respect to either frequency of injury to the right coronary artery and circumflex branch of left coronary artery or localization of the injury to this region (before or after atrial branch take-off). But patients with atrial fibrillation significantly more often had heart failure (55.1% versus 18.5%, P<0.001) and three vessel disease (30.5% versus 20.4%, P=0.05) as well as mitral valve insufficiency (20.4% versus 10.2%, P<0.05). In conclusion, in patients with coronary disease, systolic heart failure may be more important than atrial ischemia in causing atrial fibrillation.