" It’s a big complex muscle, it beats and it beats, thirty million times a year. If it lasts twenty-seven hundred million beats, which is ninety years, we call it old age. If it lasts only eighteen hundred million beats, sixty years, we call it premature heart disease. We call it America’s biggest health problem, but really all we’re saying is sooner or later, it just stops going. "

― Lee Child , Tripwire (Jack Reacher, #3)