The _________ (ECG or EKG) is a non-invasive clinical way to measure heart function. Electrodes on the wrists, ankles and chest measure the electrical activity from the heart. These are not single-cell recordings, like we studied with neurons, muscles and pacemaker cells. These are summed potentials at a distance. The events in an ECG relate to the phases of the cardiac cycle, and changes are associated with various heart disease states.