ECG trace and healthy heart. Computer artwork of a normal human heart, with an electrocardiograph (ECG) readout superimposed. The green ECG trace shows a healthy heartbeat. As a pump the heart circulates blood around the body. Main blood vessels which service the heart are seen at top, with smaller coronary arteries branching on the heart surface. The ECG heart trace measures the pumping of the heart as a series of small and larger waves. These waves correspond to electrical activity of heart muscle when it contracts and relaxes. This ECG measurement is an important means of diagnosing heart diseases like coronary heart disease, thrombosis, and arrhythmias.