Chronic atrial fibrillation (AF) is common in patients with mitral stenosis (MS). Because AF induces electrical and mechanical remodeling of the left atrium, left atrial (LA) compliance is likely to be changed in its presence. This study was performed to investigate the influence of AF on LA compliance in patients with moderate to severe MS. Data were analyzed for 356 patients (282 women; mean age 40 +/- 11 years; range 17 to approximately 71) who were registered in the percutaneous mitral commissurotomy database. Mean LA pressure was lower (21 +/- 7 vs 26 +/- 8 mm Hg; p <0.001), but LA volume was higher in the AF than sinus-rhythm group (126 +/- 62 vs 74 +/- 27 ml; p <0.001), indicating higher LA compliance, which was further confirmed by lower LA v wave at catheterization in the AF group (27 +/- 9 for AF vs 32 +/- 10 mm Hg for sinus rhythm; p <0.001). In conclusion, the presence of AF has a significant influence on LA compliance in patients with moderate to severe MS.