The aim of the study was to analyse cardiac rhythm after mitral valve replacement and to define pre-operative predictive factors for persistence of atrial fibrillation. METHODS The study group consisted of 76 consecutive pts (54 F, 22 M), mean age 54.8 +/- 8.2 (38-71) years in whom mitral valve replacement was performed due to mitral stenosis (15 pts), regurgitation (18 pts) or mixed lesion (43 pts). The prevalence of AF after the procedure was analysed with relation to age, gender and the following preoperative echocardiographic parameters: left atrial size, mitral valve area, mitral regurgitation, tricuspid regurgitation and left ventricular ejection fraction. RESULTS Chronic AF was present in 51 pts (67.1%) before the procedure and in 34 pts (44.7%) after 17.3 +/- 11.9 months (6-46) follow-up, p<0.005. Patients with AF after operation had larger left atrium size (58.6 +/- 10.9 vs 51.3 +/- 10.1 mm, p<0.005) and lower ejection fraction (53.8 +/- 7.9 vs. 59.9 +/-8.4%, p<0.01) as compared with pts in sinus rhythm. Among 51 pts with preoperative chronic AF, 21 pts recovered to sinus rhythm (subgroup I) and 30 pts remained in AF (subgroup II) after operation. The only significant differences between subgroup I and II were: higher prevalence of mitral regurgitation (85.7 vs 60%, p<0.05), larger mitral valve area (1.4 +/- 0.3 vs 1.1 +/- 0.6 cm2, p<0.025) and higher ejection fraction (58.9 +/- 7.3 vs. 53.4 +/- 8.4%, p<0.025) in subgroup I. CONCLUSIONS 1. The prevalence of AF diminishes significantly after mitral valve replacement. 2. Patients with pure mitral stenosis are at higher risk of remaining in AF after operation. 3. Preoperative left atrial dimension and LV ejection fraction are the most important predictive parameters for persistence of AF.