What is the thickest layer of the heart?

The thickest layer of the heart is the myocardium. This muscular layer is responsible for the heart's contractile function, allowing it to pump blood effectively throughout the body. The myocardium's muscular structure is essential for generating the force necessary to propel blood into the circulatory system, and its thickness varies in different parts of the heart, being especially prominent in the ventricles due to the increased workload required to pump blood to the lungs and the rest of the body.

The endocardium, another layer, lines the heart chambers and is much thinner than the myocardium, primarily serving as a smooth surface for blood flow. The pericardium is a protective sac surrounding the heart, but it is not directly involved in the pumping action. Finally, the epicardium is the outer layer of the heart wall, serving as a protective barrier, and, like the endocardium and pericardium, does not contribute to the muscle mass necessary for contraction. Consequently, the myocardium stands out as the predominant layer in terms of thickness and functional importance in the heart's physiology.