Cardiology technologists operate electrocardiogram equipment and use medical imaging technologies to record cardiac activity of patients to aid in the diagnosis, monitoring and treatment of heart disease. Electrophysiological diagnostic technologists operate electroencephalographic, electromyographic and other electrophysiological diagnostic equipment to assist physicians in diagnosing diseases, injuries and abnormalities. Cardiology technologists and electrophysiological diagnostic technologists who are supervisors or instructors are included in this unit group. They are employed in clinics, hospitals and medical laboratories.