Keep reading as we delve into everything you need to know about a female dog's heat cycle, including symptoms and behaviors ...

Male dogs become attracted to female dogs as early as the initial stages of the heat cycle (proestrus) through estrus. The whole period may last an average of 21 days.

During heat, females are receptive to mating and release mating hormones. Male dogs, on the other hand, can mate year-round once they become fertile at about 6 months, a Hill's Pet article said.

“Generally speaking, it is safe to walk a healthy, adult dog when the heat index is 85 degrees or lower,” Dr. Sarah Wooten, a veterinary expert with Pumpkin Pet Insurance, told HuffPost.

"With dogs, it's going to be a big concern if they're left outside, especially with this heat," said Dr. Joe Snock, a veterinarian at Mount Laurel Animal Hospital.