For 30 years, Dr. Muhammad Mohiuddin removed the hearts of rats and pigs, implanted organs in monkeys, and genetically modified different animals. Last month, under his supervision, physicians successfully transplanted a pig heart into a human for the first time

The operation was scheduled for 6 A.M. on what was a particularly cold January day in Baltimore. Dr. Muhammad M. Mohiuddin was taking no chances. Leery of a scenario in which he would get stuck on the way to the hospital because of the weather, he simply spent the night there. After all, the event would be the summit of his career.

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