The body is very good at keeping blood from pooling in your legs. Your muscles do a very good job of keeping fluid from building up. It’s very bad at keeping the blood out of your upper half, because it normally relies on gravity.

When you’re upside down for that long, there’s a number of things that happen. Your organs squeeze your lungs, making it harder to breathe. Your brain starts to swell. And your heart can’t keep up with the demand to pump fluid out of the chest and head and back into your legs, and eventually fails.

Guy actually lasted a really long time. Heart failure usually happens in less than a day of being upside down.