pulse, alternate expansion and contraction of artery walls as heart action varies blood volume within the arteries. Artery walls are elastic. Hence they become distended by increased blood volume during systole, or contraction of the heart. During diastole, or relaxation of the heart, blood volume in the arteries decreases and the walls contract, propelling the blood farther along the arterial pathway. The effect is that of a pressure wave initiated by the heartbeat and traveling from the aorta, the major artery leaving the heart, along the walls of all the other arteries. It takes about a quarter of a second for this wave to travel from the aorta to the arteries in the soles of the feet. The rate of heartbeat is equivalent to the pulse rate. Usually the pulse rate is determined by counting the pulsations per minute in the radial artery at the wrist. It may also be determined at any other artery point near the surface of the body. The normal rate is 70 to 90 pulsations per minute in adults, and 90 to 120 in children. Various diseases may be indicated by changes in the rate, rhythm, and force of the pulse.