There are four stages to the heat cylce , the first proestrus will last form 4 -10 days and you will seen a bloody discharge. The second stage estrus, can last from 4-13 days and the bloody discharge will turn a pale yellowish color. This is also the time the dog can become pregnant. The third and fourth stage abor absically inactive and can last from 50-80 days. Each dog is different in the amount of time each stage lasts. I would watch for the first two stages and count eighty days from there and then make the appointment.