What structure separates the right side of the heart from the left side of the heart? Why is this structure important?

Hint: The heart is a major circulatory organ that pumps blood throughout the body. It is muscular and is made up of cardiac muscles. It is approximately the size of a closed fist.

Complete answer:
The interatrial septum of the interauricular septum is a wall of tissue that acts as a separation between the left and right atrium. The interatrial septum is a wall of tissue that lies in between the left and right atrium. It forms during the first two months of fetal development. The first stage in the development of the interatrial septum is the development of the septum primum. The septum primum is a crescent-shaped tissue which forms the first divider against the left and right atria. A thick, muscular and crescent-shaped tissue called the septum secundum forms to the right of the septum primum. The septum primum originates posteriorly whereas the septum secundum originates anteriorly. The growth of the septum secundum results in the formation of a small hole called the foramen ovale.

The interventricular septum is a wall that separates the left and the right ventricles of the heart. The interventricular septum is located obliquely backwards towards the right. It is convexly curved toward the right ventricle. The interventricular septum is thick and muscular with the exception of its upper, posterior part which is thin and fibrous.

Note:
The atria are the upper chambers of the heart.
The ventricles are the lower chambers of the heart.
The right ventricle pumps blood to the lungs and the left ventricle pumps blood to the body.
The atria receive blood when relaxed and pump out blood on contraction.