Note that left and right refers to the side in the person's body, not how it is viewed on the page.
Top chambers which receive blood under low pressure from veins.
Thin walls as little pressure is required during contraction to push blood into the ventricles.
Bottom chambers of the heart. They receive blood from the atria above.
Thicker walls which contract to pump blood out of the heart to areas of the body.
The left ventricle has a thicker muscular wall than the right ventricle as it requires more pressure to be created to pump blood to the whole body.
The right ventricle wall is thinner as it requires only enough pressure to pump blood to the lungs.
The bicuspid (left) and tricuspid (right) valves prevent the backflow of blood from the ventricles into the atria.
The semi-lunar valves prevent the backflow of blood from the pulmonary artery (right) and aorta (left) into the ventricles.
Blood passes through the heart twice in one complete circulation of the body.
Note that although this is shown as a sequence, the atria contract in unison and when full, the ventricles also contract in unison. Part of the blood is being delivered to the body, while the remainder of the blood is being transported to the lungs. This means that oxygen can be picked up from the lungs, while at the same time, blood is also being delivered to the body.