Well, I am taking an online vet assistant class and I will post the info that I have learned. This will not be word for word because I would probably get in big trouble for cutting and pasting.
There are four stages to a heat cycle and each has its own "symptoms".
Proestrus-last 3-14 days (usually lasts about 9 days). This is when swelling of the vulva starts along with bleeding from the vulva.
Estrus-last from 2-20 days (usually a week). This is when the female allows breeding. Her discharge changes from red to clear or pink.
Diestrus-This is when some dogs who haven't been bred go into false pregnancy.
Anestrus-hormonal dormancy between heat cycles.
Hope this helps and sorry for the sentence fragments.
