Pyometra is a serious and potentially life-threatening infection of the uterus that commonly occurs in unspayed female dogs and cats. It is characterized by the accumulation of pus within the uterine cavity, often resulting from hormonal changes and bacterial infection. Symptoms may include lethargy, increased thirst, vomiting, and a swollen abdomen. Prompt veterinary treatment, often involving surgery, is crucial for the affected animal's survival.