Roxy never went into a visible heat. I kept waiting so that I could spray her, Cozy, and Zoey all at once but it never came. She eventually was big enough weight wise to spay. My vet said she had to be 4 pounds
at least. She was 2.5 years old when they got spayed I think. He said she was too trim to have a heat like a little female athlete- All muscle and no fat
. She still is now, too.