At the beginning phase of being in heat, called proestrus, a female cat utters short, low calls and exhibits restlessness and a greater need for affection for one or two days. As the cycle advances, she then enters estrus, or the second stage of heat, where she is sexually receptive. During this period, she meows loudly, and in some cases nearly constantly, for a period of four to six days.
When she has reached the period of sexual receptivity, a cat in heat meows strikingly loudly, almost sounding as though she is in pain. This sound is deliberate and is intended to attract neighboring tomcats for mating. Throughout the entire estrus cycle, the cat is more affectionate than usual, weaving in and out of the legs of humans, shaking her pelvis repeatedly and rolling on the floor.
After estrus, a cat enters interestrus where she rejects mating for a period of seven to 14 days. If pregnancy occurred during estrus, she delivers kittens in about 63 days. If she is not pregnant, she enters a pseudo-pregnancy phase that lasts around 36 days.
Due to dramatic changes in cat behavior during estrus, some new cat owners think something is wrong with their cats when they enter this phase. For this reason and to prevent unwanted kittens, spaying is often a good option.