ECG trace with healthy heart & chest. Colour X-ray image of a human chest with a computer-enhanced image of a heart (red, lower centre), and an electrocardiograph (ECG) readout superimposed. The ECG traces show a healthy heartbeat. The lungs are coloured blue. The heart pumps blood around the body through the main arteries and veins which are visible at its tip. ECG heart traces measure the pumping of the heart as a series of small and larger waves. These waves correspond to the electrical activity of heart muscle during contraction. This measurement is an important means of diagnosing heart diseases like coronary heart disease, thrombosis, and arrhythmias.