Why did he die in "Philomel Cottage"?

Question

"Philomel Cottage" is a short story by Agatha Christie which was recently identified as the answer to a story-ID question on our site. After seeing it there, I read the story in full - it's only 10 pages, freely available online, and thoroughly worth the time.

At the end of the story,

Gerald Martin, or Charles Lemaitre, is found dead in his chair.

This does not seem to fit the dream Alix had before:

She saw her husband lying dead and Dick Windyford standing over him, and she knew clearly and distinctly that his was the hand which had dealt the fatal blow.

But what's less clear is how he actually died. Alix has just told him a story in which

she plays the role of the "female Bluebeard", making him think that she poisoned his coffee. But it doesn't seem that she actually did such a thing: she was instead waiting for Dick Windyford to come and save her. So, what really happened? Did he simply die of fright?

Answer 1

The answer was in the locked drawer. Amongst the reports in the newspaper clippings was one which read:

The personality of the man and his extraordinary power over women had been discussed at great length in the English papers at the time, together with an account of his excitability in court, his passionate protestations, and his occasional sudden physical collapses, due to the fact that he had a weak heart, though the ignorant accredited it to his dramatic powers.

The 'ignorant' were indeed incorrect to think he was faking the collapses. In times of stress his weak heart made itself known and when in mortal fear of his life, it killed him.