In the USA, a higher incidence of cardiac disease has been reported in male Standardbreds than in females. It is unclear whether this relationship is attributo any difference in athletic requirements in horses of different sex. In other breeds, there is little documented evidence that any cardiac disease processes are more common in either sex. Rupture of the aortic root is reported primarily in aged stallions (see section 6.10.1). However, the influence of the sex of an animal on its use as an athlete or as a breeding animal is a much more significant consideration.