An electrocardiogram is a test that measures the electrical activity of the heartbeat. With each beat, an electrical impulse, or wave, travels through the heart.
This wave causes the muscle to squeeze and pump blood from the heart. A normal heartbeat on ECG will show the timing of the top and lower chambers.
The purpose is to evaluate heart function, to determine the presence of abnormal electrical impulses and to detect heart damage. No special preparation is needed prior to having an electrocardiogram.