Researchers at New York University transplanted pig hearts into two brain-dead people over the last month, the latest in a string of developments in the long quest to one day save human lives with animal organs. The newest experiments come after a historic but failed attempt earlier this year to use a pig’s heart to save a dying Maryland man. Tests with the deceased may prove an important stepping stone as regulators consider whether to allow rigorous studies of pig heart or kidney transplants in living patients.