Cardiology is a branch of medicine dealing with disorders of the heart as well as parts of the circulatory system. The field includes medical diagnosis and treatment of congenital heart defects, coronary artery disease, heart failure, valvular heart disease and electrophysiology. Physicians who specialize in this field of medicine are called cardiologists, a speciality of internal medicine. Pediatric cardiologists are pediatricians who specialize in cardiology. Physicians who specialize in cardiac surgery are called cardiothoracic surgeons or cardiac surgeons, a speciality of general surgery.
Although the cardiovascular system is inextricably linked to blood, cardiology is relatively unconcerned with hematology and its diseases. Some obvious exceptions that affect the function of the heart would be blood tests (electrolyte disturbances, troponins), decreased oxygen carrying capacity (anemia, hypovolemic shock), and coagulopathies.
All cardiologists study the disorders of the heart, but the study of adult and child heart disorders are through different training pathways. Therefore, an adult cardiologist (often simply called "cardiologist") is inadequately trained to take care of children, and pediatric cardiologists are inadequately trained to take care of adults. The surgical aspects are not included in cardiology and are in the domain of cardiothoracic surgery. For example, coronary artery bypass surgery (CABG) and cardiopulmonary bypass are both surgical procedures performed by surgeons, not cardiologists. However the insertion of stents, pacemakers and valves are performed by cardiologists.
Cardiology is a speciality of internal medicine. To be a cardiologist in the United States, a three-year residency in internal medicine is followed by a three-year fellowship in cardiology. It is possible to specialize further in a sub-speciality. Recognized sub-specialities in the United States by the ACGME are cardiac electrophysiology, echocardiography, interventional cardiology, and nuclear cardiology. Recognized sub-specialities in the United States by the American Osteopathic Association Bureau of Osteopathic Specialists (AOABOS) include clinical cardiac electrophysiology and interventional cardiology.