Cardiologists in Amsterdam are medical specialists dealing with disorders of the human heart and blood vessels. They diagnose and treat congenital heart defects, coronary artery diseases, heart failures, valvular heart disease and specialize in electrophysiology. They are concerned with the normal functionality of the heart and deviations from a healthy heart. The popular procedures used to counter coronary diseases are interventions through angioplasty, stenting, coronary artery bypass surgery, and enhanced external counterpulsation. The devices used are stethoscope, pacemakers, defibrillator, heart-lung machine, ventricular assist device and intra- aortic balloon pump. The diagnostic tests and procedures are blood tests, echocardiogram, cardiac stress test, and electrocardiogram.