The human heart acts like a pump and contains four chambers: two atria, which receive venous blood, and two ventricles, which pump blood into the arterial system. Arteries carry blood from the heart and veins carry it back 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, low in oxygen and high in carbon dioxide, returns from the body to the right atrium of the heart via the inferior and superior vena cavae, which are the largest veins in the body. Blood flows through the right atrioventricular (AV) (or tricuspid) valve to the right ventricle. Then the blood passes through the pulmonary semilunar valve, through the pulmonary arteries and to the lungs, to oxygenate and deplete the carbon dioxide present in the blood. Blood returns to the heart via 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 pulmonary circulation. Next, blood passes through the left atrioventricular valve (also called bicuspid or mitral) and into the left ventricle. 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 blood to the body are part of the systemic circulation. Systemic blood pressure rises and falls with each heartbeat due to rhythmic blood flow. 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 in the chambers of the heart as they relax and contract...... middle of paper ...... pressure' where normal blood pressure is 120 /80 mmHg. The sphygmomanometer consists of an inflating bulb that creates extra-arterial pressure in a cuff wrapped around a subject's arm. The pressure gauge of the blood pressure monitor measures the applied pressure. Arterial sounds, called Korotkoff sounds, can be heard using a stethoscope to determine systemic blood pressure. The first loud whistling sound heard, when the cuff pressure is approximately 140-160 mmHg, is equal to the systolic blood pressure. The sound is the product of a partially blocked artery during ventricular systole. As air is released from the cuff, arterial flow becomes less turbulent and sounds fade away. When the sounds disappear, it is the diastolic pressure reading; since the artery is no longer blocked, the blood circulates freely and therefore produces no sound (Johnson 2013).