A female dog in heat typically experiences a heat cycle lasting about 2 to 4 weeks (14 to 28 days). This cycle is divided into stages:

• Proestrus: lasts around 7 to 10 days, characterized by vulva swelling and bloody discharge. During this stage, the female is not yet receptive to males.
• Estrus: lasts approximately 5 to 14 days, during which the female becomes receptive to mating and the discharge may become lighter or watery.
• Diestrus: this stage follows estrus and lasts about 60 to 90 days, during which the dog is no longer fertile.
• Anestrus: a resting phase lasting several months (about 4 months or more) before the next heat cycle starts.

Overall, the female dog is actively "in heat," meaning potentially fertile and receptive to mating, for about 2 to 4 weeks. Bleeding generally occurs in the earlier part of this cycle, typically lasting about 7 to 10 days. Most female dogs go into heat around twice a year, or every six months approximately. This variability depends on factors such as breed, age, and individual differences among dogs.