I never heard of the heart attak thing either.

i do know if that if you startlel a dog when its sound asleep... that biteing is sometimes an automatic instint to protect itself.

just like when my parents or brother wake me up when im sound asleep.
they touch my arm or start talking to me... like "yo wake up" LOL and it scares the crap out of me.. and i JERK awake.

one time my mom almost got decked in the face because i was having a nightmare....