It usually last about 23 days give or take. I just had a problem with my girl being in heat for 3 months, this is defenitely not normal and I have been working closely with my vet on this issue. She has been treated with hormones but this hasn't worked so she is scheduled to by spayed next week. It has been a nightmare. If she goes past this third week and still in heat you must take her to your vet to have her evaluated.
