Describe how blood moves around the heart

De-oxygenated blood enters the right atrium from the Vena Cava, it then passes into the right ventricle due to gravity and the contraction of the walls of the right atrium. The walls of the right ventricle then contract from the apex of the heart, forcing the de-oxygenated blood upwards out of the right ventricle into the pulmonary artery which carries the blood to the lungs. Oxygenated blood enters the left atrium from the pulmonary vein, it then drops down into the left ventricle due to gravity and the contraction of the walls of the left atrium. The blood is forced upwards out of the left ventricle into the aorta when the wall of the left ventricle contracts from the apex of the heart.