The cardiovascular system in children must cope with its own growth while catering for increased demands on it as a result of growth in all other parts of the body. The heart beats about 72 times per minute at rest, and so this becomes the average adult pulse rate. All arteries demonstrate a pulse, but they are not all accessible for observation. A way to measure the radial pulse would be to listen through the chest wall, via a stethoscope, to the heart itself, counting the heart sounds per minute. The radial pulse and the apex beat sounds should be equal in number, but sometimes the ventricular contraction is so weak that the force is insufficient to create a pulse at the wrist. The electrocardiogram records the electrical activity of the heart muscle as it occurs at skin level having passed through the extracellular tissue fluid between the heart and the body surface.