Objection. To study the three-dimensional morphological features of the mitral valve baseline in patients with atrial fibrillation (AF), as well as their dynamics after annuloplasty combined with surgical correction of AF. Material and methods. The study involved 45 patients (average age – 58 (53;62) years, 80% were male). All of these patients has long history of AF, left ventricle ejection fraction > 50%, dilated mitral annulus. The frequency of persistent and long-lasting persistent AF was 80% in total, AF experience – an average of 6 years and maximum 10 years. Left atrium volume was 140±31.6 ml. Results.We obtained the average power inverse correlation between the amount of the left atrium and the posterior mitral leaflet area (R=–0.586), and the posterior leaflet length (R=–0.624); the direct correlation between the amount of left atrium and mitral-aortic angle (R=0.487); an average power direct correlation between: anteroposterior diameter and the perimeter (circumference) of mitral valve (R=0.451), the area of mitral annulus (R=0.496), the area of posterior mital leaflet (R=0.395), at least a significant inverse correlation with the angle of posterior mitral leaflet (R=–0.289). Direct correlation was obtained between the perimeter of mitral annulus and the tenting volume of miral valve (R=0.373). After the suture annuloplasty anteroposterior diameter decreased from 36.3±2.9 to 30.9±2.4 mm (p<0.001). Anterolateral, posteromedial diameter decreased from 39.3 (37.4;40.4) to 32.4 (31;34) mm (p<0.001). Annulus height of three-dimensional shape defining rings increased from 4.5 (3.3;6.8) to 6.4 (5.4;7.8) mm (p<0.001). Also increased the level of the height of annulus from 13±5,7 to 22±8% (p<0.001). The decrease in the area of mitral annulus and perimeter was found from 1153.3±185.7 to 847.1±103.8 mm2 and from 126.6±11.7 to 109.2±8.5 mm, respectively (p<0.001). After the annuloplasty the length of anterolateral posteromedial coaptation in the projection area increased from 22 (20;26.3) to 24 (22;28) mm (p=0.036), which proves deeper coaptation. Non-planar angle declined, became more acute, and was 113 (101;119) compared with the preoperative 123.9 (113.8;146) (p<0.001). Conclusion. Atrial fibrillation leads to disruption of mitral valve, leading to valvular insufficiency, through basic mechanisms: annulodilation, reducing the height of mitral annulus level index (decrease saddle), the increase in non-planar angle (angle of the leaflets coaptation).