Why Boxer dog's die young

My 1st died from a hernia at the age of 10 and I have heard of the heart troubles causing premature death. My current has the blood documented on his papers for his heart. There was someone not too long ago that was offering free heart testing through the Vet I go to for Boxer owners. I never took mine as he is from a tested blood line and shows no symptoms. My understanding is they were bred from the bulldog and mastiff and were brought back from war by the gi`s. They were bred as a foxhole dog.