During ECG examination we deduce facts about the state of the heart from the heart’s electrical activity. The ECG machine collects electrical signals from so-called electrodes in limbs and chest.
A specialist can analyze heart function from the signs, and can reveal any abnormalities without surgery, then find the appropriate treatment for it. Are you familiar with this picture?
The ECG examination itself may be carried out by a professional assistant with appropriate qualification, but the results are analysed by an internist or cardiologist.