how long they bleed?
Usually 3-4 weeks. Keep her away from ALL male dogs – intact or not and after this heat, make an appointment with the vet to get her spayed. It's much better for her health and will guarantee that you won't have any unwanted pregnancies, which could lead to death if she escapes and mates with a large dog.

I am no expert, but I believe most dogs tend to be in heat for 3 weeks to a month.
References :
All dog's heat cycles last three weeks starting when the bleeding begings. Bleeding generally lasts anywhere from a few days to the whole three weeks depending on the position of the uterus. The middle week is the most fertile time, but they can become pregnant at anytime during the three week period. Also, don't walk your dog through your neighborhood. They will leave a scent trail for males to follow them home, and males will jump/breakdown a fence to get to a female.
References :
About 3 weeks
References :
all dogs heat cycle lasts about 21 days
References :
Usually 3-4 weeks. Keep her away from ALL male dogs – intact or not and after this heat, make an appointment with the vet to get her spayed. It's much better for her health and will guarantee that you won't have any unwanted pregnancies, which could lead to death if she escapes and mates with a large dog.
References :
My dog Mia, is a teacup yorkie and has been in her fist heat for a little over seven weeks. My vet said that it happens sometimes.. he said nothing is wrong. Should I get a second oppinion? Or is it common?