Dear Student
The heart is separated into four chambers: the right and left atria, and the right and left ventricles.
Deoxygenated blood coming back to the heart from other parts of the body enters into the right side of the heart and goes into the lungs.
Oxygenated blood from lungs enters into the left side of the heart and is pumped back out into the body.
There are valves through which blood passes before leaving each chamber of the heart. The valves prevent the backward flow of blood.
Regards