How your heart works
Your heart is basically a hollow muscular organ consisting of two pumps. Each pump (one on the left and one on the right) is divided into two chambers that are linked by passageways in which there are valves to ensure that the blood flows only in one direction. The left ventricle, which must pump blood out into the body through a large blood vessel (the aorta), is the chamber of the heart that works hardest, and; therefore, has the greatest need for oxygenated blood.
The blood’s cycle through your heart begins when oxygen-depleted blood returns to the heart, entering the right upper chamber (atrium) via the largest veins, called the venae cavae. From the right atrium, blood passes through a valve to the right lower chamber (ventricle). It is then pumped through the pulmonary artery into the lungs where it receives oxygen.
This freshly oxygenated blood then flows through the pulmonary veins into the left atrium and then into the left ventricle. From the left ventricle, blood is pumped through the aorta out into your body again.