The human heart consists of a pair of atria which receives deoxygenated blood and pumps it into a pair of ventricles which pump blood into the vessels. The right atrium receives the systemic blood from the superior and inferior venae cavae which are relatively low in oxygen and pumps it into the right ventricle which pumps it into the pulmonary circuit, lungs. Exchange of oxygen and carbon dioxide occurs in the lungs, and blood high in oxygen returns to the left atrium which pumps blood into the left ventricle which in turn pumps blood into the aorta and the remainder of the systemic circuit. The septa are the partitions that separate the chambers of the heart.
At the base of the aorta is the aortic valve which prevents backflow from the aorta. It normally is composed of three flaps. When the ventricle relaxes and blood attempts to flow back into the ventricle from the aorta, blood will fill the cusps of the valve causing it to close. This process repeats itself every second throughout the heart and one minute throughout the body.