Healthy ECG heart traces. Computer-enhanced image of many electrocardiogram (ECG) traces of the normal heartbeat. These ECG heart traces show a healthy heart rhythm. As a pump the heart circulates blood around the body. An ECG heart trace measures 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 ventriclar contraction. This measurement of wave structure and frequency is an important means of diagnosing heart diseases like coronary heart disease, thrombosis, and arrhythmias.