in heat

Idioms  

1. In a state of sexual excitement immediately preceding ovulation. For example, Our cat's in heat so we have to keep her inside. This expression applies to most female mammals and indicates the period when the animal is fertile and most receptive to mating. [Mid-1700s]

---

Example Sentences

Ground-level ozone, often called “smog,” is a corrosive gas that forms when pollution from vehicles and other sources reacts in heat and sunlight.

From Los Angeles Times • Apr. 22, 2026

Unlike internal combustion engines, which require a large temperature gap to operate efficiently, Stirling engines can run on much smaller differences in heat.

From Science Daily • Feb. 27, 2026

Weston was the only slider under 56 seconds as he clocked 55.88secs in heat two, to add to his 56.21secs in run one on the new Cortina sliding track.

From BBC • Feb. 12, 2026

An extra layer of low-moisture cheese between dough and sauce helps lock in heat for travel.

From The Wall Street Journal • Oct. 8, 2025

“Well, you can’t blame ’em in heat like this.

From "Tuck Everlasting" by Natalie Babbit