Female cats that have not been spayed eventually enter an estrus cycle, typically referred to as "heat." Pet owners should keep in mind that this is very different from heat stroke, which can also be a problem with pets in the summer time. Instead, when a veterinarian talks about cats in heat, they're most likely referring to the medical term for the behavioral changes that accompany the estrus cycle.
A cat will first enter heat when it reaches puberty or sexual maturity, which tends to be about 6 months after the cat is born. However, the exact timing can vary depending on the breed and time of year. Estrus cycles also line up with the cat's natural breeding season, which varies depending on a number of factors.
According to VCA Animal Hospitals, the breeding season for most cats extends from January to late fall. During this time period, the cat will endure multiple heat cycles. The breeding season may vary according to temperature and climate - cats in warmer parts of the country or who live almost exclusively indoors may actually have a permanent breeding season.
A cat in heat will cause a number of issues for the owner. First and foremost, the cat will naturally be inclined to try to get pregnant during this time period. The cat attracts a mate through urination. It's not uncommon for owners to see cats "marking their territory" on large vertical objects, such as trees or telephone poles. The pheromones released during this act will attract male cats. This can result in a number of unusual behaviors. Pet owners in the past have reported unknown male cats attempting to enter their house, or the female cat attempting to escape.
The female cat's behavior will likely change drastically while she is in heat. Female cats typically begin rubbing up against people or objects frequently during this time period. In addition, the cat may roll around on the floor. Most owners also report that the cat will become much more vocal, yowling in a way that many owners find irritating. The heat period may last up to a week, after which the cat will have 1-2 off weeks before starting up again.
Since estrus cycles are natural, the only way an owner can prevent this from occurring is through spaying a cat. This will end the estrus cycles and also prevent the cat from getting pregnant. VCA Animal Hospitals recommends spaying for all female cats in order to reduce pet overpopulation in the United States.