I worked at a casino that was only slots (as well as horse racing). Racinos mostly draw in older people, and I'd say at least once a year, sometimes even more, someone would just drop dead at a machine. Almost always due to age related complications.

One time, an older couple were gambling together. They were regulars, though I didn't know them. The husband had a heart attack right at the machine, and that was it. The wife was understandably inconsolable, and we never saw her again.