The meaning of American cardiology has been transformed over the past century. During that time, cardiology has been defined by several organizations: by the American Board of Internal Medicine through subspecialty certifications; by the two major American cardiology societies, the American Heart Association and the American College of Cardiology; and by the four major cardiology journals. These organizations have sometimes cooperated, sometimes competed. Cardiology has also had to negotiate relationships with several external interest groups, including pediatrics, surgery, hospitals, and internal medicine. Throughout the 20th century, the word cardiology has had no meaning save its definition within a larger web of organizations, relationships, and ideas. The meaning, like the meaning of all specialties and subspecialties, is historically mediated and constantly changing.