One-Way Valves

• One-way valves are a common characteristic of the structures of the heart that help ensure that blood does not move into areas that it shouldn't be. The one-way valves differ, however, in the structures of the atria and ventricles. The right atria has a one-way valve that allows blood to enter the ventricles but not come back into the atria. The left ventricle also has a one-way valve that works in the opposite manner, allowing blood to flow into the left atria, but not the other way around.
  
  

Size and Volume

• The atria are much smaller than the ventricles. In fact, the atria are about one-third the size of the ventricles. The left ventricle is the largest chamber of the heart. Its muscle mass is about three times that of the right ventricle. Despite this, both ventricles has similar volume capacity. The atria, however, do not share the same volume capacity as the ventricles. They are not only one-third the size, but also only have one-third the volume of the ventricles.
  
  

Structural Thickness

• The structural thickness of the atria and ventricles is another important different between the structures of the heart. The right atria is only about 2 millimeters thick. The right ventricle, on the other hand, has about a 4 to 5 millimeter thickness. The left atria is slightly larger than the right atria, coming in at about 3 millimeters thick. The left ventricle is between 8 and 15 millimeters thick, which makes sense because of how large it is compared to the other structures.
  
  

Blood Movement

• The structures of the heart differ in how they move blood. For example, the right ventricle only pumps one-eighth as hard as the left ventricle. This is because of the size and function of the left ventricle. The atria also do not have to pump as hard as the ventricles in order to move blood because of their small size, volume and thickness.