Often called internists, or doctors for adults, these are specialists in the diagnosis and medical treatment of common and complex illnesses in adults. Like GPs, they are able to act as Primary Care Physicians to adults and adolescents, providing continuing care for their patients and serving as coordinators when other medical specialists, such as surgeons, are involved. Some internists choose to focus their practice on one area of internal medicine and, therefore, take additional training in a subspecialty such as cardiology.