Mazie was a real doll and will be missed dearly by her owner, who adored her.
Aortic ruptures are a rare thing and are usually fatal in horses. In some cases if the rupture is within the heart, sometimes the horse can survive but it usually only a matter of weeks. Since they are so rare, there has been very little research done on it. They aren't able to link to much of anything like age, breed, genetics , etc. There is some that believe it might be related to a type of strongyle infestation that ruptures the wall of the vessel but it hasn't been studied to be proven.
Its just not fair.