The front view of the heart most clearly reveals the structure of this powerful muscle. The heart has four chambers surrounded by thick muscular walls. In this model, the right atrium (on your left) is shown in blue, the left atrium (on your right) in yellow, the right ventricle in purple, and the left ventricle in red. The chambers contain valves (shown in white) that prevent the blood from flowing back inside once it has been pushed out. Click on the "Front view with blood" link to see the blood in motion