What structure separates the right and left sides of the heart?

The atrial and ventricular septum is the correct structure that separates the right and left sides of the heart. The terms "septum" refer to partitions that divide the heart into distinct chambers. The heart consists of four chambers: right atrium, right ventricle, left atrium, and left ventricle.

The atrial septum specifically separates the right atrium from the left atrium, while the ventricular septum separates the right ventricle from the left ventricle. Together, these septa ensure that oxygen-poor blood from the right side does not mix with oxygen-rich blood from the left side, which is essential for the efficient functioning of the circulatory system.

Other structures, such as the myocardium, are important for the heart's muscular contraction and function, but they do not serve the purpose of separating the heart's sides. The coronary sinus is a collection of veins that drains blood from the heart itself but is not involved in separating the heart's chambers. The interventricular septum is a specific part of the atrial and ventricular septum that separates the ventricles, but it does not encompass the entire separation function of both septa.