Which heart layer forms the inner lining of the heart chambers and valves?

• A. Endocardium
• B. Epicardium
• C. Myocardium
• D. Pericardium

Answer: (A)

The inner lining of the heart chambers and valves is the endocardium. This thin layer is made of endothelium (a simple squamous epithelium) with a supporting connective tissue layer, forming a smooth surface that contacts the blood flow and helps reduce friction as blood moves through the chambers and across the valves. Its continuity with the endothelium of the great vessels also explains why the same type of lining lines both the heart interior and the vessels.

The epicardium is the outer layer, also called the visceral pericardium, which covers the heart's surface. The myocardium is the thick, muscular middle layer responsible for the heart’s contractions. The pericardium refers to the fibrous sac surrounding the heart, providing protection and anchoring.