A male chihuahua named "Heart-kun" has been born on May 18, 2007 with a perfect heart shaped marking on his back. Shop owner Emiko Sakurada said that this is the first time a puppy with these marks had been born out of a 1,000 that she has bred.
He is soooooo cute!!
Follow Heart-kun, here's a news clip on a cat with a heart-shaped mark as well.
I've tried to find more info about this heart-shaped marking cat, but...