system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: If a patient is having open heart surgery and dies on the table, since there is no heartbeat, how does the surgeon know?
gpt
Well, speaking as someone who has participated in *MANY* open-heart surgeries, death would not be called on the heart-lung perfusion machine, as it is performing the gas exchange and fluid propulsion functions of the heart and lungs.

If something happens, it would be after coming off the perfusion machine and after getting the heart to restart with an electrical cardioversion -- electrical shock directly to the heart tissue. It is almost always successful. So death would be called either if the heart could not be restarted (rare), or if the heart failed after having restarted.