A dog can come in to heat usually after six months regardless of whelping. She can have same gap between 2 heat cycle whether after giving birth or without pregnancy. First stage of canine heat cycle is called proestrus when bleeding starts and vulva swells. Second stage is called estrus when bleeding is reduced and dog show flagging and mating takes place. Third stage is called diestrus that can be of 57-58 days in case of pregnancy and 60-100 days if no pregnancy. Fourth stage is called anestrus that can last for 4-5 months.