I owned a puppy who was misdiagnosed with an enlarged heart by an emergency vet. I took him to a cardiologist who explained in vet school...they are given heart diagrams (essentially pictures) and use those as a comparison. She said as a breed ...yorkies have larger hearts.
But we all know that don't we?
For the kennel cough...use a warm mist vaporizer or take puppy into a steam filled bathroom. The warm steam helps a great deal.