Objective To map and compare the right atrium in patients with AF to those with atrioventricular nodal reentrant tachycardias (AVNRT, as control group) and to investigate the anatomical and electrophysiological abnormality of the right atrium in AF.Methods The anatomy and electrophysiology of right atrium and cavotricuspid isthmus were evaluated in 20 patients with AF (16 M/4 F, mean age 55.9±10.68 years) and 26 patients with AVNRT (9 M/17 F, mean age 47.50±19.56 years) during coronary sinus pacing at 600 ms prior to ablation with electro-anatomical mapping system. Right atrial volume (RAV), the length and width of cavotricuspid isthmus (IsL, IsW), unipolar and bipolar voltage in the right atrium (UniV-RA, BiV-RA) were measured and compared between patients with AF and those with AVNRT. Results RAV, IsL, IsW, UniV-RA, and BiV-RA were 143.22±40.72 vs 104.35±21.06 ml, 39.31±8.10 vs 32.42±9.77 mm, 30.54±7.48 vs 23.15±6.61 mm, 1.96±1.24 vs 1.53±0.91 mv and 1.47±1.47 vs 1.29±1.12 mv in AF and AVNRT respectively.Conclusion The right atrial volume is larger; both the length and width of cavotricuspid isthmus are greater. Unipolar and bipolar voltages in the right atrium are higher in AF than in AVNRT, suggesting that the enlarged right atrium, increased length and width of cavotricuspid isthmus, and concomitant atrial hypertrophy are important substrates for initiation and perpetuation of typical AF.