Pyometra is a disease mainly of middle-aged dogs and cats that have not been spayed. The uterus becomes infected (by bacteria from the vagina), inflamed and greatly enlarged. Pyometra follows a heat cycle in which fertilization did not occur. It is caused by an excessive quantity of progesterone, or an oversensitivity to it.
The word "pyometra" is derived from latin "pyo" meaning pus and "metra" meaning uterus. The pyometra is an abscessed, pus-filled infected uterus. Toxins and bacteria leak across the uterine walls and into the bloodstream causing life-threatening toxic effects. Without treatment this is fatal.