[Moonman62]

The coroner later said Carol was in her home office and the cause of death appeared to be a heart condition called mitral valve prolapse (MVP).

...

That’s a very rare cause of death, but it can happen.

https://www.heart.org/en/health-topics/heart-valve-problems-and-disease/heart-valve-problems-and-causes/problem-mitral-valve-prolapse

[shelterguy]

I had a cousin who was in her mid thirties when it happened to her. No symptoms at all.