Mortality data
The mortality data suggests a USA 50 year old male has about 1 chance in 200 dying in a year, whereas the data for a guy who had bypass surgery is about a chance in 50.
Although flying is increased stress (7000 foot cabin pressure is a factor) the chances while flying are still pretty low, but -- big but -- the chances of a death of a guy who had not have the operation is about 4 times less.
Google can help you refine these numbers but they are at least in the correct zip code if not on the right street.