My first female cat I did not get spayed right away and I don't think she ever went into heat. She was almost a year old. If she went into heat I never knew it. Now Mama Kitty, who showed up as a stray, once she weaned those kittens there was no mistaking that she was in heat...WOW. Needless to say we got her fixed ASAP. My husband would call me at work and say this is what I have been listening to ALL day and I could hear her in the background yowling. I don't know if all of them act that way but I am assuming they do, which makes me think my older girl never went in to heat before.
"It's really the cat's house--we just pay the mortgage." ~ Unknown