When cats are in heat, they exhibit a variety of behavioral and physiological changes. Female cats in heat may become unusually clingy, frequently emit high-pitched cries, sometimes resembling a baby's cry, and experience a decreased appetite. They may also urinate frequently, rub against people or objects, and may even display courtship postures such as raising their hindquarters and holding their tails up.

When male cats are in heat, they will exhibit increased territoriality, frequently urinating indiscriminately around the house to mark their territory. They may also become more aggressive and anxious, and sometimes even try to escape from the house to find female cats.