Background and Objectives: Scar-related intra-atrial reentrant tachycardia is rare in patients without prior atrial surgery. Electrophysiologic study(EPS) could localize a critical area responsible for intra-atrial reentrant tachycardia and radiofrequency ablation. Of 32 consecutive atrial tachycardias(AT) which underwent electrophysiological studies and radiofrequency ablation in our institution, 5 patients(4 men, mean age 47짹18) with AT having reentrant nature on clinical EPS basis and complicated fragmented electrogram were studied. Results:Two patient had prior open heart surgery( 1 in ASD, 1 in TOF ). The other 3 patients had dilated cardiomyopathy with no prior surgery. Electrophysiological studies and endocardial mapping found (1) AT cycle length was 256짹24 ms; (2) AT had induction and termination by atrial extrastimuli or rapid atrial pacing in all; (3) Adenosine(10짹6mg) did not terminate AT in all; (4) Exit sites of AT was right atrial free wall (4 of 5) and inferoposterior right atrial septum near coronary sinus os(1 of 5); and (5) Earliest activation site had timing relative to P wave by -57 짹 29 ms, and concealed entrainment pace mapping had shortest stimulus-P interval 29 짹 7 ms. (6) Intracardiac electrogram showed fragmented potential of high frequency and low ampltude in all patient and successful ablation site was abutting the fragmented electrogram zone. By the concealed entrainment pace mapping technique, radiofrequency energy (6 짹 4 pulses) successfully eliminated all clinical AT (follow-up, 13짹7 months). with recurrence in one patient 4 months later, which was also cured by RF ablation. CONCLUSIONS: AT observed in cardiomyopathic patient might be scar-related intra-atrial reentrant AT. Radiofrequency ablation energy delivered to a critical area in the atrial reentrant circuit guided by EPS is safe and effective for the treatment of intra-atrial reentrant tachycardia.