What is the wall that separates the left and right sides of the heart called?

The wall that separates the left and right sides of the heart is known as the septum. This structure is crucial because it divides the heart into two distinct halves, preventing the mixing of oxygenated blood from the left side with deoxygenated blood from the right side. The septum plays a vital role in maintaining efficient circulation and ensuring that each side of the heart can function effectively in pumping blood to the lungs and the rest of the body. By keeping the blood flow separate, the septum helps optimize oxygenation and support overall cardiovascular function.

The other options refer to different anatomical structures or functions related to the heart. The pericardium is the protective sac surrounding the heart, the myocardium is the muscular layer responsible for the heart's contraction, and the endocardium is the thin lining of the heart chambers. Each of these structures has its unique role, but they do not serve to separate the left and right sides of the heart like the septum does.