Answer
The three layers of the heart are the epicardium, the endocardium, and the myocardium.
The epicardium covers the external heart surface and has a layer of adipose tissue in some areas.
The endocardium lines the internal heart surface. It doesn't have a layer of adipose tissue.
The myocardium is the thickest layer and performs the work of the heart.
Work Step by Step
Epicardium from epi- "surface" or "above" and cardium "heart". This layer is a simple squamous epithelium overlying a thin layer of areolar tissue. This layer contains some adipose tissue and the largest branches of the coronary blood vessels travel through it.
Myocardium from myo- "muscle" and cardium "heart". This is the literal muscle of the heart. The thickness is proportional to the workload of the individual chambers (left ventricle is thickest). The myocardium has muscle spirals which form the myocardial vortex.
The endocardium from endo- "inside" and cardium "heart". This is another simple squamous epithelium layer of tissue overlying a thin areolar tissue layer. There is no adipose tissue in this layer. The endocardium is also continuous with the endothelium of the blood vessels.
