Many large breed dogs die tragically each year from a condition lay people like me refer to as Bloat. It has been my experience, throughout the years, that the vast majority of my clients profess complete ignorance of this potentially tragic condition.
I strongly recommend asking your veterinarian to explain this condition to you, as well as advising you whether or not your particular breed tends to have a greater potential for it. Remember, far better to be informed and not need it then to need it and not be informed