Healthy ECG heart trace. Computer-enhanced image of an electrocardiogram (ECG) trace of the normal heartbeat, with a human heart seen in the back- ground. The ECG heart trace shows 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. ECG is an important means of diag- nosing heart diseases like coronary heart disease, thrombosis, and arrhythmias.