Personality Changes

• Female dogs may attract neighborhood male dogs by flagging.Jupiterimages/Brand X Pictures/Getty Images
  
  Just like women, most female dogs will have noticeable changes in their personality before they go in to the estrus cycle. Each dog is different and while some seem to be short tempered and cranky, others will act lethargic or become very affectionate. Watch your dog closely, and you will likely see behaviors that indicate she may be getting ready to go into heat. Some females will also rub their hind quarters against furniture or walls. This is referred to as "flagging."
  
  

Body Changes

• A veterinarian can tell you if a dog is in heat.Apple Tree House/Lifesize/Getty Images
  
  Another visible change you can see is in the female dog's vulva. It will show signs of change when she is in estrus and appear to be larger and swollen. You can also check her teats to see if they appear slightly bigger. These may have a noticeable change in color and look more pink than usual.
  
  

Bleeding and Urination

• You may notice blood if your dog is in heat.BananaStock/BananaStock/Getty Images
  
  You may notice small amounts of blood on your dog's bedding or other places where she has been lying or sitting. Bleeding will occur in the early days of your dog's estrus or heat cycle. Bleeding will start as a dark red color, but as the cycle continues, the discharge will change to pink and sometimes to tan before stopping. This indicates your dog is closer to being ready to breed. Female dogs also begin to urinate more when in heat. It is their way of telling all the male dogs in the area that she is ready for them. A male dog can pick up her scent from quite a distance and may start to frequent your yard waiting for her. If you notice strange male dogs hanging around more than usual, it may be that your female dog is in heat.
  
  

Veterinarian Tests

• The signs that your female dog is in heat can be very visible with some dogs and harder to detect in others. The best way to tell if your pet is in heat is to take her to the veterinarian and have her progesterone tested. This is a simple blood test that detects whether this hormone level is elevated, which would indicate that the dog is in heat.