Pyometra is a isease of the uterus most commonly seen in female dogs, but also seen in queens (female cats), rabbits, ferrets, rats and guinea pigs. Pyometra is an important disease to be aware of for any dog owner because of the sudden nature of the disease and the deadly consequences if left untreated. It has been compared to acute appendicitis in humans, because both are essentially empyemas within an abdominal organ.