Healthy ECG heart trace. Computer artwork of an electrocardiograph (ECG) readout of the normal heartbeat over an abstract heart. This ECG trace shows a healthy heart rhythm. As a pump the heart circulates blood around the body. ECG heart traces measure this pumping of the heart as a series of small and larger waves. These waves correspond to the electrical activity of heart muscle during contraction: the smaller wave corresponds to atrial contraction, the taller wave to ventricular contraction. This measurement of wave structure and frequency is an important means of diagnosing heart diseases including coronary heart disease, thrombosis and arrhythmias.