The human heart works like a pump and is made up of four chambers: two atria, which receive venous blood, and two ventricles, which pump blood into the arterial system. Arteries carry blood away from the heart and veins carry blood to the heart. The atria are the upper chambers and the ventricles are the lower chambers of the heart. The blood flow is as follows. Blood, with a low oxygen content and a high carbon dioxide content, returns to the right atrium of the heart from the body through the inferior and superior vena cava, which are the largest veins in the body. Blood flows through the right atrioventricular (AV) (or tricuspid) valve to the right ventricle. The blood then passes through the pulmonary semilunar valve, through the pulmonary arteries, and into the lungs, to oxygenate and reduce carbon dioxide in the blood. Blood returns to the heart through the pulmonary veins and into the left atrium. This path of blood from the right ventricle of the heart, through the lungs, and back to the left atrium of the heart is called the pulmonary circulation. Then, blood passes through the left atrioventricular (also called bicuspid or mitral) valve and into the left ventricle. The blood is then pumped through the aortic semilunar valve and into the aorta, which is the largest artery in the human body, and supplies the body with oxygen-rich blood. The arterial branches of the aorta that supply this blood to the body are part of the systemic circulation. Systemic blood pressure rises and falls during each heartbeat due to the rhythmic flow of blood. A cardiac cycle is a period of time that extends from the end of one heartbeat to the end of the next. During each cycle, pressure changes occur within the chambers of the heart as they relax and counteract… center of paper… pressure' where a normal blood pressure is 120/80 mmHg. The sphygmomanometer consists of an inflatable bulb that creates extra-arterial pressure in a cuff wrapped around the subject's arm. The pressure gauge on the sphygmomanometer measures the pressure applied. Arterial sounds, called Korotkoff sounds, can be listened to through a stethoscope to determine systemic blood pressure. The first loud hissing sound heard, when the cuff pressure is around 140-160 mmHg, is equal to the systolic blood pressure. The sound is the product of a partially occluded artery during ventricular systole. As air is released from the cuff, arterial flow becomes less turbulent and sounds fade. When the sounds disappear, this is the diastolic pressure reading; since the artery is no longer occluded, the blood flows freely and therefore does not produce any sound (Johnson 2013).