Catheter-based, right and left atrial compartmentalization procedure was evaluated using a noncontact mapping (NCM) system. Its usefulness to identify and close discontinuities in linear lesions in both atria was evaluated. The impact of linear lesion continuity on ablation success of chronic AF was also investigated. Nineteen patients with symptomatic, drug refractory chronic AF were studied. Right atrial ablation with three predefined lines was attempted in all patients. In 18 patients, left atrial ablation was performed with four linear lesions. During a follow-up of 12 +/- 3 months, 6 of 19 patients remained in sinus rhythm (SR) without antiarrhythmic agents (AAs). In addition, four patients were maintained in SR with AA. Thirteen of 14 patients with gaps identified during off-line analysis had recurrence of AF. Only one patient with a gap was free of recurrence without AAs. In the remaining five patients without recurrence of AF, no gap was observed during off-line analysis. In all four patients who were free of AF with additional treatment of AAs, two gaps had been identified. In the remaining nine patients with chronic AF recurrence, a mean of 4.9 gaps were identified. Excluding the initial learning period (first five patients) the success rate increased to 43% (6/14 patients) without and to 71% (10/14 patients) with AA. NCM identifies discontinuities in lines of ablation. Successful ablation of chronic AF is associated with continuity of linear lesions and good clinical technique demands a vigilant search for and closure of every gap.