40 seems a bit young to be dying from atherosclerosis.
“Atherosclerosis usually starts in the teens and 20s, and by the 30s we can see changes in most people,” says cardiologist Matthew Sorrentino MD, a professor at The University of Chicago Medicine. In the early stages, your heart-related screening tests, like cholesterol checks, might still come back normal.
But over the years, this problem tends to slowly get worse. By the age of 40, about half of us have cholesterol deposits in our arteries, Sorrentino says. After 45, men may have a lot of plaque buildup. Signs of atherosclerosis in women are likely to appear after age 55.”
Link: https://www.webmd.com/heart-disease/features/atherosclerosis-your-arteries-age-by-age
In 1978 my 33 year old husband died from it.