Female cats (called "queens") are termed "seasonally polyestrus." This is because their multiple heats are influenced by seasonal changes in the amount of daylight. Cats usually have heat cycles between January and September. Starting around January, a female cat will keep coming back into heat every 7-10 days until she is bred or the amount of daylight decreases (usually around October). Cats kept indoors and exposed to artificial lights may cycle year-round.
The stages in a cat's estrus cycle include:
anestrus, proestrous, estrus, interfollicular (interestrous stage), and diestrus.
Anestrus is typically seen in the short days of winter. During this time, the queen does not go through any "heats." The tom is not attracted to the queen, and vice versa.
Once she starts cycling, proestrus may last 1-2 days in some queens, or just a few hours. It is not consistently seen. During this stage, the queen is very vocal, repeatedly calling for a male cat. The male cat is attracted to the queen, but she will not let the tom near her. She will roll on the ground and constantly rub against furniture or your leg. The bleeding seen in female dogs during proestrus is not seen in female cats.
Estrus lasts about a week, but may be longer or shorter. During this time, the cat exhibits the same signs as in proestrus. She will assume a breeding posture with her head and front legs near the ground and the rump area held high. You may notice her urinating frequently. During estrus, the queen will allow the tom to approach her and mate. Mating may last 1-20 seconds. The queen may allow more than one tom to mate with her, so it is possible for a litter of kittens to have different fathers. This is called superfecundation.
If she was not bred, the queen will enter an interfollicular stage (also known as interestrus). She shows no sign of reproductive activity during this stage. This stage may last about 1 week. She then goes into proestrus and estrus again. If she mated and ovulated but did not become pregnant, she goes through a diestrus stage that lasts about 5-7 weeks. During this stage, she does not show signs of reproductive activity, but may appear to be pregnant. If the mating was successful, she will go through an approximately 63-day pregnancy.
In cats, puberty usually occurs between 6 and 9 months of age. Cats may start having estrus and become pregnant as young as 5 months of age.
Spaying your cat will eliminate all the signs of being in heat and potential pregnancy. It will also eliminate the risk of certain diseases including ovarian cancers and infections of the uterus, and will greatly decrease the risk of mammary cancer.