Dogs : The first heat cycle in dogs usually occurs around 7 to 8 months of age and is signaled by swelling of the vulva and a bloody vaginal discharge (though the discharge can be quite variable from breed to breed). The entire cycle is about 3 weeks from start to finish. Most dogs repeat their cycle about every 6 months.

Cats : The first heat cycle in cats usually occurs around 6 to 7 months of age. The cat may often be seen rolling on the floor or ground and become extra affectionate towards their owner. She may be more vocal and actually scream very loudly. This behavior may persist for 5 to 8 days followed by a period of quiescence of the same duration. This behavior may then repeat 5 to 8 times or until she is bred by a male cat.