Circumferential radiofrequency ablation around the orifices of the pulmonary veins is a curative catheter-based therapy of paroxysmal and persistent atrial fibrillation (AF). Three-dimensional cardiac image integration is a promising new technology to visualize the complex left atrial anatomy and neighbouring structures. This study aimed to validate the accuracy of integrating multislice computed tomography (MSCT) into three-dimensional electroanatomic mapping (EAM) to guide radiofrequency catheter ablation (CA) of AF. Forty consecutive patients (34 male, mean age 56 +/- 10 years) with multidrug-resistant AF underwent 16-slice MSCT 1 day before radiofrequency CA. MSCT data were processed and imported to the Cartotrade mark EAM system. Using the CartoMergetrade mark Image Integration Module, the generated EAM was aligned with the MSCT images. An integrated statistical algorithm provided information about the accuracy of the fusion process. In every single patient, MSCT images could be aligned with the EAM. Mean distance between the EAM points (n = 63 +/- 14) and the MSCT surface was 1.6 +/- 1.2 mm with no difference between sinus rhythm versus AF (p = 0.145) and no distinction between patients in paroxysmal versus persistent/permanent AF despite a significant difference in left atrial diameters. An average of 388 +/- 81 radiofrequency ablation points were taken within the procedures resulting in a mean distance of 2.3 +/- 1.8 mm between the EAM points and the MSCT image after the ablation procedure. There was a significant difference of alignment accuracy before and after radiofrequency CA (p < 0.001). MSCT images can be accurately integrated into three-dimensional EAM. Pre-interventional cardiac rhythm does not influence the precision of fusion. Accuracy of fusion deteriorates after radiofrequency CA.