In an attempt to test whether the higher numbers of cardiovascular deaths were simply a statistical blip or a genuine sign of the effect of traveling into deep space, the scientists exposed mice to the same type of radiation that the astronauts would have experienced. After six months, which is the equivalent of 20 human years, the mice showed damage to arteries that is known to lead to the development of cardiovascular disease in humans.
Well, no. The scientists slammed the mice with ~6-12 months' worth of radiation in ten minutes. Yeah, they probably had artery damage. Stuff like that happens when you stick a mouse in the microwave.