There are four valves which control the blood flow through the heart. They all consist of two or three flaps which swing open to allow blood through with each heart beat, and swing closed to prevent blood going back in the wrong direction.
Deoxygenated (blue) blood returning from the body collects in the right atrium. It flows to the right ventricle through the ‚tricuspid valve‘. It is then pumped through the ‚pulmonary valve‘ into the pulmonary artery on its way to the lungs. Oxygenated (red) blood returning from the lungs collects in the left atrium and flows through the ‚mitral valve‘ into the left ventricle. It is then pumped through the ‚aortic valve‘ into the aorta and to the body.