How should I tell if my dog is in heat?

Non-spayed female dogs will go into heat usually twice a year, and can start as early as 6 months old. A female dog may appear nervous, easily distracted, and more alert than usual. She may urinate more often than she normally does. Her behavior may change due to the shift in her hormone balance. She may initiate sexual interactions with other dogs, elevate her hind quarters toward males when they approach, deflect her tail to one side and tense her rear legs. There may be discharge and swelling.

She will start to bleed and other dogs, particularly male dogs will be much more interested in her. It would be wise to keep her away from other dogs during this time, as some dogs may become aggressive. There are also diapers for the blood to keep it from getting all over your floor. It will start with a few drops and then boom! You'll know.