My Tiger Lily is just coming up to 6 months old, and is booked in for her spay on the 28th, but as luck would have it she started to go into heat yesterday. I noticed right away; lots of licking of the bottom, rolling around, walking kind of squatted down (very funny to watch!), and yowling. Our poor neutered male, Sox, has no idea and she keeps trying to be friends with him, lol, it's hysterical!
Anyhow, I spoke with our vet who said it's no problem for her to be neutered even while in heat.