RIP Michael S. Hart: founder of Project Gutenberg

What was the cause of death? It isn't mentioned in his obituary or any of the news items I've seen so far.

The previous discussion of Michael's death is at <a href="http://news.ycombinator.com/item?id=2971971" rel="nofollow">http://news.ycombinator.com/item?id=2971971</a>