The July, 2014 Airline Pet Travel Report contains pet incidents for the month of May, 2014.
On American Airlines flight 2312 from Dallas, TX to Seattle, WA, a dog named Robert was found unresponsive upon arrival in Seattle, WA. American Airlines reports, that after arrival in Seattle, the dog was taken to the vet where he was pronounced dead. The cause of the death is unknown, thus American Airlines took no preventative measures.
Source: July 2014 Air Travel Consumer Report.