Which tissue separates the right atrium from the left atrium?

The atrial septum is the correct answer because it is the wall of tissue that divides the right atrium from the left atrium in the heart. This thin layer of muscle and connective tissue is critical for maintaining proper blood flow and preventing the mixing of oxygenated and deoxygenated blood. The right atrium receives deoxygenated blood from the body through the superior and inferior vena cavae, while the left atrium receives oxygenated blood from the lungs via the pulmonary veins. The atrial septum plays a vital role in the proper functioning of the heart, ensuring that each chamber performs its specific role effectively.

The ventricular septum, on the other hand, separates the right and left ventricles, not the atria. The myocardium refers to the muscular tissue of the heart responsible for its pumping action, and the pericardium is the protective sac surrounding the heart. Therefore, while these other options are related to heart anatomy, they do not specifically separate the atria.