A 2-year-old female intact American Bulldog was presented to the Cornell University Hospital for Animals Emergency and Critical Care Service for evaluation of brown-red mucoid vulvar discharge, 6 months after having a litter by cesarean section. An open pyometra was diagnosed by ultrasound and vaginal cytology. The bitch was admitted to the hospital and medically managed with intravenous fluids, antibiotics, anti-nausea medication, prostaglandins, and pain medication. After 4 days of hospitalization, she was discharged to her owner as she was no longer producing vaginal discharge, the fluid in her uterus had decreased and she had transitioned to oral medications. Two months after her discharge, she was started on mibolerone for 2 months to prolong the time until her next heat. She came back into heat 2.5 months after stopping the mibolerone. This paper will discuss the canine estrous cycle, pyometra and medical management of the condition.