['Localized sites of high frequency during atrial fibrillation (AF) are used as target sites to eliminate AF. Spectral analysis is used experimentally to determine these sites. The purpose of this study was to compare dominant frequencies (DF) with AF cycle length (AFCL) of unipolar and bipolar recordings.', 'Left and right atrial endocardial electrograms were recorded during AF in 40 patients with lone AF, using two 20-polar catheters. Mean age was 53+/-9.9 years. Unipolar and bipolar electrograms were recorded simultaneously during 16 seconds at 2 right and 4 left atrial sites. AFCLs and DFs were determined. QRS subtraction was performed in unipolar signals. DFs were compared with mean, median, and mode of AFCLs; 4800 unipolar and 2400 bipolar electrograms were analyzed. Intraclass correlation was poor for all spectral analysis protocols. Best correlation was accomplished with DFs from unipolar electrograms compared with median AFCL (intraclass correlation coefficient, 0.67). A gradient in median AFCL of >25% was detected in 16 of 40 patients. In 13 of 16 patients (81%) with a frequency gradient of >25%, the site with highest frequency was located in the left atrium (posterior left atrium in 8 patients). The site with shortest median AFCL and highest DF corresponded in 25% if unipolar and in 31% if bipolar electrograms were analyzed.'] Does dominant frequency of atrial fibrillation correlate poorly with atrial fibrillation cycle length?