KIM KARDASHIAN blogged that her "heart is completely broken" . . . because her 4-month-old kitten Mercy died.  Mercy was a gift from KANYE WEST, but she had to be put down after being diagnosed with a fatal, cancer-like virus.

Kim actually didn't even own the cat anymore.  A few weeks after getting it, Kim developed allergies, and would have needed to get regular injections to combat them . . . so she gave Mercy to KHLOE'S assistant.