Dr. Leonard Bailey turns 74 in August, but as chief of surgery for Loma Linda University’s Children’s Hospital, about 60 miles east of Los Angeles, he still puts in 60-hour weeks, starting at 6:30 every morning. Tall and slender with blue eyes and a corona of thinning gray hair, the pioneering heart surgeon performed the world’s first successful infant-to-infant heart transplant and has done hundreds of transplants for the tiniest of babies.

“Some weeks, it’s 80 to 90 hours, if we do a transplant that goes round the clock, but we seldom do more than two a day,” says Bailey of his workload. Despite his hectic schedule, he has no plans to retire. “There’s no reason to stop. If you’re constantly thinking new thoughts and dealing with new problems, it refreshes your brain cells and makes new connections.”