What Can We Do about ours fighting Cats?

We have 3 cats. A mutured 11/2 year old male. a non-spayed 2 year old female and a 3 year old fenale.
Recently past few days, the two females have not been getting alone.
In fact they have been fighting, so we have been having to isolate them in different rooms. The non-sprayed female is in heat and she seems to be the agressor in most instances. But up until now they always got along reasonsbley well.
What could be the cause of this sudden behavioral changes, and what can we do to get them to at least tolerate each other, without having to put them in separate rooms or get rid of one of them?
Answers:
well you have one male and two females? i think that the females are fighting over the male like two males can fight hours on end over one female.it is natural. and since they have been separated then they may have got used to being away from the male and not be interested any more. like in human nature. a girl could like a man one day and be arguing the next then make up and then argue...get the point!? it is probably just a mating faze. (they had better be neutered!) :0)
No worries Hun XXXXX

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hormones are the likely cause of her aggression because she is in heat and especially because there's a male around. you should get her spayed. the best idea is to get them all spayed but since one is especially aggressive focus on her for now.

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Hormones can be a bi tch. Get them spayed and I bet the behavior will improve greatly

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Get the one that is the aggressor spayed, she is in heat and that's why she is acting this way, take her to the vet for neutering and you'll notice the difference in her behavior, when you bring her home. Once they are all neutered they'll get along again like they did before, Hope this helps.

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let them get used to eachother or get them all nutered

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get them all neutered cats can get REAL nasty and it hurts when u get involved!