Which layer of the heart wall contracts and is composed primarily of cardiac muscle tissue?

The layer of the heart wall that contracts and is composed primarily of cardiac muscle tissue is the myocardium. This thick muscular layer is responsible for the heart's pumping action, generating the force needed to circulate blood throughout the body. The unique structure of cardiac muscle tissue, with its intercalated discs and branching fibers, allows for synchronized contractions, which is crucial for efficient heart function.

In contrast, the endocardium is the innermost layer lining the heart's chambers, composed of endothelial cells that contribute to a smooth surface for blood flow but do not have muscle fibers for contraction. The epicardium serves as the outer layer of the heart wall and is made up of connective tissue and a layer of mesothelial cells, providing protection and serving as a conduit for blood vessels and nerves. Lastly, the pericardium refers to the fibrous sac surrounding the heart, providing stability and reducing friction, but it does not participate in the contraction of the heart.