Which layer of the heart's wall is composed of cardiac muscle?

The layer of the heart's wall that is composed of cardiac muscle is known as the myocardium. This layer is essential for the heart's ability to contract and pump blood effectively throughout the body. The myocardium is located between the epicardium, which is the outermost layer, and the endocardium, which lines the interior of the heart chambers. The presence of specialized cardiac muscle cells within the myocardium allows for the coordinated contractions that are vital for maintaining proper circulation and ensuring that the heart functions as an effective pump. This is why the correct answer is focused on the myocardium, emphasizing its critical role in heart function.