In contrast to the sequential mapping systems such as the conventional and the electroanatomic mapping, the non-contact mapping provides simultaneous mapping. The non-contact-mapping system detects far-field endocardial potentials from a multielectrode-array catheter and reconstructs over 3,000 unipolar virtual electrograms. Based on the virtual electrograms, the system produces an instantaneous three-dimensional (3-D) isopotential map. High-density mapping of the endocardial activation sequence allows immediate and simultaneous identification of a propagation vector along the line and the identification of an arrhythmogenic focus on a single beat. The methods and results of different ablation strategies for atrial fibrillation using the non-contact-mapping system are reported.