As a muscular organ, the heart has two pumps that are divided into an upper chamber (atrium) and lower chamber (ventricle). These chambers are linked by passageways with valves to ensure blood flow in one direction. The lower left ventricle works the hardest, pumping blood into the body through the aorta, the largest artery in the body. In turn, this chamber of the heart has the greatest need for oxygenated blood.
The blood’s cycle through the body begins when oxygen-depleted blood returns to the heart, entering the upper right atrium via the largest veins (venae cavea). Blood passes through a valve from the right atrium to the lower right ventricle. The blood is then pumped through the pulmonary artery into the lungs where it receives oxygen.
Freshly oxygenated blood then flows from the lungs through the pulmonary veins into the left atrium and then into the left ventricle. From the left ventricle, blood is pumped through the aorta to supply the body.