 The heart receives blood with low oxygen from the body. It pumps this blood to the lungs where it receives oxygen. Back to the heart now and then back out to the body. There are these four stations in the heart which orchestrate the process. We call them the right and left atrium and the right and left ventricle. Now that we've seen them in 2D, let's move to a schematic 3D model. Here again are our four chambers, right atrium and ventricle and left atrium and ventricle. Here are the lungs down the back. The blood arrives at the right atrium. When the heart is relaxed, blood flows passively into its adjacent ventricle, the right ventricle. The ventricle contracts with great force to push blood out toward the lungs. Changing colour as it does so, the blood receives oxygen and comes back to the heart. Toward the left atrium it comes. This blood then fills the adjacent ventricle when the heart is relaxed. That's the left ventricle. Contraction of the ventricle ejects blood to the body. From the body to the right atrium, from the right ventricle to the lungs. From the lungs to the left atrium, from the left ventricle to the body. Onto our more realistic model. This is the right atrium here, the right ventricle, the left atrium and the left ventricle. And away it goes. The contraction of the ventricles is what you can feel when you put your hand on your left nipple, beating away every second of every hour of every day you're alive. This video was made possible by support from Beauty Within Medicine, a social enterprise dedicated to making medical education better and more socially accountable. Click below to learn more.