Tragedy at the track as three horses died Thursday night during the Rangeland Derby.

The accident took place on the backstretch involving 2009 Derby winner Chad Harden’s four horses; One of the lead horses went down causing the crash involving all the horses.

Stampede spokesperson Doug Fraser tells 660News it appears a medical condition may be to blame.

“The left lead horse, which was the horse that originally collapsed, experienced a fatal event, the nature of which is undetermined at this time. The right lead horse and the outrider horse were humanely euthanized due to the severity of their injuries.” said Fraser.

The fourth horse suffered serious injuries and Harden is said to be pretty shaken up from the ordeal.