After a doctor completes medical school and is licensed to practice medicine, the physician may pursue a rigorous, 3-year training program in Internal Medicine. After passing an examination and completing the requirements, the doctor is Board Certified in Internal Medicine, and is called an Internist. This is different from an intern, who is a doctor who has completed medical school and is in the first year of postgraduate training.
Cardiology is a subspecialty of Internal Medicine. Cardiologists (heart specialists) complete two additional years of training in diagnosis and treatment of all types of heart disease after completion of Internal Medicine training. Interventional cardiology is further specialization in the field of cardiology, requiring one more year of training in catheter-based interventions for ischemic heart disease and other cardiac problems.