In my case, my "stiff heart" is apparently the result of cardiac amyloidosis. The V and A walls are stiff and enlarged. My QRS on an ECG are showing a sawtooth pattern less than .5 mv. I know I am a candidate for sudden death if the amyloid fibrils get into the sensori-command nerves between the brain and heart. And my valves are trying to work, but the macular tissue coverings on the valves is causing them to misfire frequently with PVCs. Every valve of every kind in my body, it seems, has been invaded by fibrils and macular covering. Urinary, larynx, stomach, cardiac, kidney, everything. So have your SERUM, plasma and urine checked for misfolded protein, especially if you are over 50.