A rotor and a stator assembly, wherein the rotor comprises at least one stage of rotor blades and the stator comprises at least one stage of turbine stator vanes. By providing pacing stimulation to the left atrium during ventricular systole, a beneficial effect is obtained which can prevent or reduce the extent of mitral regurgitation. According to one important embodiment of the present invention, the thickener particles are co-dispersed with particles of one or more particulate UVR-filters such as titanium dioxide, zinc oxide, or SUNSPHERE, and most preferably with the natural particulate sunscreens such as the metal oxides.