It's space week at One Cracked Fact. You know that that means. Facts … in … SPAAAAAACCCEEEE!

Apollo 15 marked the fourth time we landed on the Moon. The two astronauts walking on the lunar surface were David Scott and James Irwin, and all seemed well, right up until mission control looked at Irwin's vitals and realized he'd just had a heart attack.

Well, we're calling it a heart attack, which is a nonscientific term. What we had was a kind of arrhythmia, where the heart alternates between beating too fast and skipping a beat ("bigeminy"). These are symptoms that would generally make a doctor conclude the something had messed with blood flow in the coronary arteries. At no point did Irwin clutch his chest and gasp in pain, but many people who have heart attacks never do that.

NASA did not inform anyone in the crew about what they'd noticed. Irwin's heartbeat returned to normal, and the mission continued as planned. Two years later, he had his next heart attack, a major one. He had a few other heart attacks during his remaining years, and a final attack killed him at 61, making him the first and youngest moonwalker to die. 

Why didn't NASA tell the crew about Irwin's shaky heart the moment they saw it, and recall the men straight back to Earth? Well, for starters, they wanted the men to complete their mission—which involved retrieving some floating space film—and in the end, they succeeded, without Irwin keeling over in space itself. Perhaps that doesn't justify NASA leaving the info out of the mission docs, even after Apollo 15 returned to Earth.

There was another reason, though (or, maybe you can call this just mission control rationalizing their decision). On Earth, they would put someone with that heart rhythm in the ICU, but in his space suit, Irwin kind of already was in an ICU. He was already on oxygen. And he was in low-gravity, which is perhaps the best state for reducing strain on the heart. It was possible that moonwalking, spacewalking, and zooming back down were actually the best heart treatment known to science. 

For more Moon secrets, check out:

Read The Doodles Of The Apollo 11 Astronauts

6 Terrifying Real Speeches That Were Thankfully Never Given

The Felt-Tip Pen That Won the Moon

Top image: NASA

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