On average, in the first stage of heat, the vulva will begin to swell and there will be a blood-stained discharge, your bitch will usually be interested in the males which are attracted at this time but will not accept them for mating. This stage usually lasts for about 9 days. In the second stage, often specifically referred to as the heat phase of the oestrus cycle because the female is actually receptive to mating and will stand for the male in order to do this.