Atrial fibrillation and mitral valve insufficiency often occur together. Mitral regurgitation is a known cause of atrial fibrillation related to the volume overload of the left atrium due to ventricular remodeling in ischemic heart disease, dilated or arrhythmogenic cardiomyopathy. Functional failure develops on valves with no organic pathology. It is mainly caused by an increase in the size of heart chambers. Secondary or functional regurgitation develops on the background of the fibrous ring dilation, due to dilatation of the heartchambers. Mitral regurgitation may gradually deteriorate in the long-term period. Patients with moderate mitral regurgitation may be asymptomatic for a long time and have insignificant hemodynamic changes over the years; however, regurgitation progresses due to the volume overload. Progression of the mitral regurgitation is a variable process. It depends on the progression of fibrous annuli sizes. Dilatation of the left atrium (especially caused by atrial fibrillation) is caused by dilatation of the mitral ring and leads to the mitral valve insufficiency. In patients with permanent atrial fibrillation fibrous rings of atrioventricular valves are dilated to a greater extent. Patients with severe tricuspid valve insufficiency may have more increased sizes of the fibrous rings of atrioventricular valves compared to patients without tricuspid regurgitation. We give a case-based pathophysiological explanation of severe mitral and tricuspid valve insufficiency caused by an isolated dilatation of the fibrous ring on the background of long-standing persisting of atrial fibrillation. Annulodilatation, the left ventricle dysfunction following virtually all methods of treatment of arrhythmia in this case are the factors leading to severe mitral and tricuspid regurgitation, requiring surgical correction aimed at reducing the size of the ring. This correction, as shown by our monitoring, can be effective in the midterm period and suggests good long-term results.