How soon will a female dog go into heat again if breeding fails?

Under normal circumstances a female dog comes into heat twice a year. If breeding fails, she will go into heat again on her normal schedule, which means the next heat will come after about half a year. Female dogs usually go into heat once in spring, around March to April, and once in autumn, around September to October.

To improve the success rate of breeding, you can mate the dog twice. After the first mating, breed her again about 48 hours later, which can increase the likelihood of a successful pregnancy.