Ventricles have thicker muscular walls because they need to pump blood with greater force to various organs in the body, whereas atria mainly facilitate blood collection and transfer to the ventricles.

When the right ventricle contracts, it pumps deoxygenated blood to the lungs for oxygenation.

Deoxygenated blood returns from the body to the heart through the right atrium, which then contracts to transfer it to the right ventricle.

The left ventricle receives oxygenated blood from the left atrium and pumps it out to the body when it contracts, ensuring that vital organs receive oxygenated blood.

The left atrium receives oxygen-rich blood from the lungs and then relaxes to allow for the collection of this blood before it is transferred to the left ventricle.