This is when the female cat is receptive to the male. External signs such as a swollen vulva are not as obvious in the cat as they are in the dog. The main signs are behavioral; loud vocalizing, rolling on the floor, elevating the hindquarters, and possibly a decrease in appetite. Many people have confused the signs of the feline estrus phase as signs of being in pain. Length: 3 to 14 days (average of one week). If the female is not mated, she may go back into heat within several days.

The first estrus cycle usually occurs by age 6 to 12 months; for some cats as early as 4 months of age, for others not until age 12 months or so. Cats can get pregnant during their first heat cycle, but this is not advisable as a 6-month old cat is not yet fully grown/mature, and complications for the mother and the kittens are more likely. An intact (not spayed) female cat of reproductive age is called a queen.