The normal heart is divided into 4 chambers:

• right atrium
• left atrium
• right ventricle
• left ventricle

The chambers on the right side of the heart receive unoxygenated blood from the veins ("blue" blood). The chambers on the left side pump oxygen-rich ("red") blood out of the heart to the rest of the body.
Four valves act as one-way doors to direct blood flow:

• aortic valve (left side of the heart)
• mitral valve (left side of the heart)
• pulmonary valve (right side of the heart)
• tricuspid valve (right side of the heart)

A wall (septum) divides the right and left side of the heart.

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