An electrocardiogram is a non-invasive test to determine how the heart is functioning by measuring the electrical activity of the heart. In the normal heart, each heart beat is initiated by an electrical impulse in the upper right heart chamber at a location known as the sinus node. From here, an electrical wave of activity spreads over the entire heart through an electrical conduction system producing characteristic waveforms on an ECG. These waveforms can be interpreted by a doctor to diagnose a variety of heart disorders.