Evanson 

Cardiologists are medical doctors who specialize in the diagnosis and treatment of diseases or conditions of the heart and blood vessels, such as 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 they perform certain treatment procedures. 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). Also, they may specialize in treating specific age groups, such as a pediatric cardiologist, who only treats children.