A 34-year-old man with permanent atrial fibrillation (AF) underwent electrophysiologic testing. Spontaneous AF was observed even after successful pulmonary vein (PV) isolation of all four PVs. Intracardiac electrograms recorded from a basket catheter deployed around the crista terminalis during triggered atrial premature beats exhibited low-amplitude potentials which were suggested to reflect focal ectopic activity, preceding high-frequency atrial potentials. The firing from those focal activity sites induced a shift in the breakout sites and conduction block to the right atrium, which suggested the participation of preferential conduction. Radiofrequency catheter ablation targeting the focal origin and preferential conduction sites eliminated the AF. ©2006, The Authors.