Studying heart disease in astronauts yields clues but not conclusive evidence

When James Irwin suffered his first heart attack at age 43 — just two years after walking on the moon — NASA doctors dismissed any connection with his trip to space, during which he had experienced short spells of irregular heart rhythm.

"They noted that pre-flight testing had shown Mr. Irwin to be prone to slight uneven heartbeats on occasion after exercise," according to the New York Times. But then Irwin died of a heart attack in 1991, when he was just 61. A year earlier, fellow Apollo astronaut Ron Evans died of a heart attack in his sleep at age 56. And Neil Armstrong died after complications from cardiovascular surgery in 2012. He was 82.