When a female dog is in heat, it means she has reached sexual maturity and is ready to mate. During this time, her body will produce hormones and release them into the bloodstream which will attract male dogs from miles away. The most common signs of heat include bloody discharge from her vulva, increased urination, and swelling of the vulva. Other signs include changes in behavior such as being more clingy, increased whining, and licking herself. Male dogs can detect the pheromones released by a female dog in heat, and they will be attracted to her. It is important to note that dogs do not have periods like humans do, but they go through an estrus or heat cycle a few times per year. During this time, female dogs are receptive to mating and could become pregnant. If you have an unspayed female dog, it is important to know the signs of a dog in heat to prevent unwanted pregnancy.