“Segregationist”, by Isaac Asimov (1967)
In the aftermath of robots (“metallos”) being granted legal equality
with biological humans, a transplant patient is offered the choice of
a partly-organic heart or a fully mechanical one. He chooses the
mechanical one, because it’ll last longer — but the surgeon
disapproves of cyborgization, saying that humans and metallos should stick to their own kind. TWIST ENDING: the surgeon is a metallo.
This story was written several months before the first successful
human-to-human heart transplant, and it’s interesting that Asimov
chose to portray the procedure as a minor background detail. It’s also intriguing that, in 1967, he had characters who found segregation to be viscerally repugnant. But ultimately, this is a very minor Asimov.