This stage of heat can last from 4-20 days. The average is 7-10 days. There are 3 common signs for a dog in heat during this stage:

 

Swollen Vulva:

This is one of the best ways to spot the beginning of a dog heat cycle. The swelling is a significant difference over her “normal” appearance. Her teats may also swell slightly, but this is not a great heat indicator and can be tricky to spot.

 

Discharge:

Your female may suddenly spend a lot of time licking herself. Take a tissue and wipe her vulva. If you notice red discharge, and her vulva is swollen, that’s a pretty good indicator that your dog is definitely coming into heat. It’s important to check this, since timing is everything when it comes to mating (or preventing a mating) your dog. The first day you notice the bloody discharge is called "DAY 1". Mark it on your calendar.

 

Suitors

The third sign of heat is not found on your dog, but in the presence of other dogs. You may notice neighbor dogs hanging out around your house. They can smell your female's heat cycle. You may notice that your dog will tuck her tail often, protecting herself. She is not ready to accept a sire.

 

The Estrus Stage of the Dog Heat Cycle typically last from 5-14 days.

During this time your dog is fertile (her actual heat). At this stage, the discharge typically changes from red to straw colored. In many dogs it’s still somewhat pink, but you will notice a definite difference in color from the beginning of proestrus.

This change usually occurs around day 8 or 9. Your dog will also be willing to accept a sire during this stage. She will switch her tail to the side. She may whimper and try to be outside more often than is normal for her. She is following her instinct to breed. Keep a close eye on her. Even if she is in a kennel, she can still end up pregnant