The author deals with three causes of mitral regurgitation (MR) – in infectious endocarditis of mitral valve, in dilatation cardiomyopathy and in hypertrophic cardiomyopathy. Mechanism an characteristics of a group of the three causes is non-homogenous. MR in infectious endocarditis is organic (primary) and arises due to acute destruction, perforation or deformation of leaflets with vegetations localized on hypotensive side of valvular leaflets. MR in dilatation cardiomyopathy is a typical functional regurgitation without any organic changes on valvular apparatus of mitral valve and is the consequence of left ventricular disease, remodelation and changed spatial relations of mitral apparatus. Mitral regurgitation in hypertrophic cardiomyopathy has a specific mechanism and is the consequence of morphological changes of suspensory apparatus and dynamics in obstruction of left ventricular outflow tract.