Final answer:
The endocardium is the innermost layer of the heart wall that lines the chambers and valves, connected to the myocardium by connective tissue.
Step-by-step explanation:
The innermost layer of the heart wall is known as the endocardium. This layer is made up of a simple squamous epithelial layer called endothelium and is responsible for lining the chambers of the heart where blood circulates, as well as covering the heart valves.
It is connected to the myocardium, which is the middle and thickest layer of the heart wall, with a thin layer of connective tissue. The myocardium consists mainly of cardiac muscle cells that are essential for the pumping action of the heart, while the outermost layer is the epicardium, a part of the pericardial covering of the heart.