Because dogs go into heat generally twice a year, a dog will go into heat approximately 4 to 6 months after giving birth, according to WebMD. This can vary greatly with different breeds.
Larger dog breeds go into heat much less often, with a typical span of 12 to 18 months between normal cycles. Smaller dog breeds are much more regular, with 3 to 4 months between each cycle. A mother dog who is nursing puppies will not go into heat, and if she is to be spayed, the surgery should wait until after the pups are weaned and before she goes into heat again.