Animation of a beating heart, transparent to show its interior. The heart comprises four chambers, each controlled by a valve that prevents blood flowing the wrong way. Deoxygenated blood from the body flows into the right atrium, and from there through the tricuspid valve to the right ventricle, which pumps it to the lungs. The newly-oxygenated blood passes from the lungs to the left atrium, then through the bicuspid valve (mitral valve) to the left atrium, which pumps it around the body. This clip is also available on black (K004 5204) or with a transparent alpha channel background (K004 5205).