The heart is a muscular organ that pumps blood through the body. It has four chambers: two atria and two ventricles.
The right atrium receives deoxygenated blood from the body through veins. It then pumps it into the right ventricle, which pumps it into the pulmonary artery and lungs to pick up oxygen-rich blood returning from the lungs.
The left atrium receives oxygenated blood from the lungs via the pulmonary veins; it then passes this blood into the left ventricle, which pumps it into circulation through arteries.
The heart also contains valves that keep blood flowing in one direction, ensuring that it does not flow backward through the heart.
Learn the heart anatomy with free labeled diagrams.