When we visited my parents lately, we learned about the circumstances of my father's heart problem, who was diagnosed with "cardiac amyloidosis" last year. These are protein threads that are deposited in the heart muscle and thicken and stiffen it. You can read more about it [https://www.escardio.org/Journals/E-Journal-of-Cardiology-Practice/Volume-19/cardiac-amyloidosis-epidemiology-diagnosis-and-therapy|here].  This disease is also a case of an excess of "malformed" proteins, such as can occur in the blood or in various organs. Proteins are - in general - information and building materials with a variety of functions.

The link contains interesting information about this disease - for example, there are 2 main types, one genetic predisposition and a "wild type" that often affects men over 65. That it is quite common or underdiagnosed, and that it can affect various heart structures - the heart wall (myocardium), coronary vessels, heart valves and also the conduction system. So there can be several conflicts and nuances involved that allow or "require" such modifications. 

My parents still love each other and have stuck together through thick and thin. In recent years (especially since the Covid years) you can see that my mother is deteriorating, including mentally, while my father is mentally fit but physically weaker. And they are both afraid of "mental decline" in particular; my grandmother and her sister both got Alzheimer's in old age. And I don't think my mother is developing it at all, but that she is so used to stressing herself that her brain shuts down and she forgets things. And she then puts herself down and triggers herself again and again. And my father stands next to her and can't help her because she's so caught up in herself. And it annoys him, and they trigger each other, and both are afraid. 
I find the clinical picture of amyloidosis in the heart totally logical! A chronically recurring -self-esteem conflict about not being able to help that is certainly being resolved at times, but not properly and sustainably. A heart that keeps getting bigger, but also "hardens". How often does something like that happen in older married couples?! 

When we "children" talk to him, it does my father good and he pulls himself together. We bought my mother a device for vagal stimulation and encourage her to do all rhythmic and creative activities she can resonate with. We strengthen both of their self-esteem as best we can, and we want them to focus on enjoying life...