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The focus of the circulatory system is the heart---- the chief pumping tool composed of muscle; the left side of the heart has two linked compartments i.e. the left atrium and the left ventricle. The right side of the heart also has two associated compartments i.e. the right atrium and the right ventricle. The right and left sides of the heart work collectively. Blood moves in the heart via two large veins referred to as the inferior and superior vena cava, pouring oxygen-deficient blood from the body into the right atrium. The pulmonary vein pours blood (laden with oxygen) from the lungs into the left atrium. Blood moves from the right atrium into the right ventricle via the open tricuspid valve and moves from the left atrium into the left ventricle through the open mitral valve. Blood departs from the heart via the pulmonic valve, into the pulmonary artery and to the lungs. Blood departs from the heart through the aortic valve, into the aorta and to the body. This procedure happens in a recurrent manner, affecting blood to pour constantly to the heart, lungs and body.