Can cats go into heat while they are pregnant?

Pregnant cats can go into heat. According to About.com, a pregnant cat can go into heat and even conceive a second litter, which she carries at the same time as the first.

LoveToKnow Cats advises keeping pregnant cats indoors because of the risk that they could go into heat again and conceive a second pregnancy. According to About.com, some signs that a female cat is in heat include the cat becoming increasingly affectionate, licking her own genitals, calling out loudly to attract a male cat and assuming the mating position, where the head is down and the rear quarters are raised.