Estrus

n. heat, state of sexual activity (Zoology)

Oestrus is also the biological genus name of the gadfly. The estrous cycle (also oestrous cycle; originally derived from Latin oestrus) comprises the recurring physiologic changes that are induced by reproductive hormones in most mammalian placental females. Humans undergo a menstrual cycle instead. Estrous cycles start after puberty in sexually mature females and are interrupted by anestrous phases. Typically estrous cycles continue until death. Some animals may display bloody vaginal discharge, often mistaken for menstruation.
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Es·trus or oes·trus n. The periodic state of sexual excitement in the female of most mammals, excluding humans, that immediately precedes ovulation [more]Estrus - Community and Resources

Noun
1. applies to nonhuman mammals: a state or period of heightened sexual arousal and activity
(synonym) oestrus, heat, rut
(antonym) anestrus, anestrum, anoestrus, anoestrum
(hypernym) physiological state, physiological condition

The phase of the estrous cycle when a cat is fertile (commonly called "heat").

The phase of the female reproductive cycle when the dog is fertile (commonly called "heat").