Cardiologists are medical doctors who specialize in the diagnosis and treatment of diseases or conditions of the heart and blood vessels, such as chest pain (angina), irregular heart rhythms, high blood pressure, heart failure, or heart attacks.

Cardiologists administer tests that show how well a person's heart is working, such as a treadmill test (exercise electrocardiogram), and perform procedures such as cardiac catheterization and angioplasty. They can further specialize in interventional cardiology (the use of mechanical treatment methods, such as angioplasty) or electrophysiology (treatments involving the heart's electrical system) and may also specialize in treating specific age groups, such as a pediatric cardiologist, who only treats children.

Cardiologists can be board-certified through the Board of Internal Medicine, which is recognized by the American Board of Medical Specialties. Pediatric cardiologists are recognized by the American Academy of Pediatrics.