Hellooo, so this answer is gonna be a little rambling but like most of my headcanons I like loosely basing this stuff on real biology except dialed up to eleven. So I usually give pre-heat stage symptoms similar to pms and a sharp drop of estrogen like headaches, insomnia/fatigue, fluctuating appetite etc and the actual heat would be like a cranked up ovulation since that is the biological drive of these cycles even if the story wasn’t about breeding kink lol. But I also say “loosely” because if all omegas (regardless of primary gender) are menstruating we run into a slight timing problem. Pre-heats are usually when we make the characters suffer right before they get what they need during their heat, but realistically if you are ovulating during a heat your pre-heat would be when you are feeling Good because there is an increase in hormones again. If I make pre-heat essentially pms there should normally be several days between the period and ovulation and yet in fics pre-heat is sometimes only hours before the real thing, so that’s where the fantasy comes in!! Similar for pre-ruts, we can take symptoms of rising testosterone in preparation to a potential mating like increased libido, high bp, also insomnia, aggression, mood swings etc. But the case for ruts is way easier because I don’t have to math out where and when the uterine lining for the potential pups is going lmao (this goes for female alphas too, because I like basing biology on second gender more than first since that’s the point of this universe, like a female alpha doesn’t have a womb in my head and they do have cocks although smaller than male alphas because of some level of estrogen from their primary gender, think of it almost like being on HRT. Same for male omegas, they have wombs but also t-dicks unlike female omegas etc etc. What about betas? Hm I think maybe they are more intersex and their genital traits vary widely and depends on the specific individual/plot). Hopefully that answered your question I confuse even myself sometimes djkshdjka