heart sounds at night, they are very audible but now I hardly hear the beats

I am 76 and at nigths,in bed, my heart was very ,very audible(could hear quite well the sound, and some time a missing beat).Now I hardly hear the beats.I was diagnosed with some walls of the heart a bit thick(probably the effect of years of blood pressure?).The fact that my heart is not pounding like before could be because it is "slowing" down in its work, is "giving up"?