Technically, there is no such thing as a Cardiology "residency." To become a Cardiologist, you must complete a residency in Internal Medicine, which is 3 years. Then, you must apply to a general Cardiology fellowship program, which is an additional 3 years. There are also additional sub-specialties within cardiology: Interventional Cardiology, Electrophysiology (EP), and Advanced Heart Failure Cardiology. Each sub-specialty requires an additional fellowship of approximately 1 year and each has its own board exam.