Blue died very suddenly and we think painlessly. She was sleeping and let out a whimper. When Sarah went in the room she was dead. We think it was from old age. She was 11, had arthritis and was a little over weight. They didn't do an autopsy so it's left to our discretion. I also think it may have had something to with her heart as she had really bad breath which means she had a lot of build up on her teeth...and this build up has a bacteria in it that is known to cause heart failure in older dogs if swallowed. Either way it wasn't expected and she went quickly in her sleep.