My yorkie hasnt been in heat yet but they way that I tell my chihuahua is going into heat is she will start to lick that area alot(yuck!
). She doesnt really swell much so its hard for me to tell that way and she barely bleeds. BUt my boxer- holy cow!!! Thats another story. She swells so much its crazy!! so needless to say, I can always tell when she is going to start. PLus she has a "smell" about her.