This cat(s) is/are called Frank and Louie, and (by now) 13 years old it is the longest living two-faced cat ever. He/They live(s) in Massachusetts, in the care of a loving woman only known as Marty. He/They suffer(s) from a condition called Disprosopus, a genetic disease that caused him to grow two faces. This malfunction is not only found in cats but also in other animals. The latest case noted in a human was the Indian girl Lali Singh, who unfortunately died two months after birth of a heart attack.
Watch a video with an interview with pet owner Marty here: http://www.youtube.com/watch?v=9dYFwpQZ9Gg
Article in the LA Times: http://articles.latimes.com/2011/sep/30/news/la-heb-two-faced-cat-diprosopus-20110930