What's not well known is that, during the Apollo 15 mission, Lunar Module Pilot James Irwin almost added his own name to the list.

He had undetected and severe coronary artery disease and developed bigeminy while on the way to the Moon. If he wasn't in the pure oxygen and zero-G environment of the Apollo Command Module, that would have had a good chance to progress to full on fibrillation and zero blood pressure.

The coronary artery disease was only detected two years later when he had a major heart attack (at the age of 43!) and was given an emergency triple bypass.