Inner Visceral Layer (aka Epicardium): adhering tightly to the surface of the heart
The pericardial cavity sits between the 2 layers of the pericardium. It contains pericardial fluid which allows easy movement of the heart wall against its covering. The heart wall is covered externally by visceral pericardium, the epicardium. The thick middle layer of the wall of the heart is composed of cardiac muscle and is known as the myocardium. Internally, the heart wall is the endocardium. The endocardium is continuous with the endothelial lining of the blood vessels.
Gross Anatomy of the Heart
The base of the heart is formed by the thin-walled atria which are externally separated from the ventricles by an encircling coronary groove or atrioventricular groove. Each atrium ends in a free, blind-ending auricle. The large region, or apex of the heart if formed by the ventricles which are also firmer due to the greater thickness of their walls. The left and right ventricles are defined by shallow grooves called the interventricular grooves which descend toward the apex.
Internal Anatomy of the Heart
Right Atrium
The greater part of the right atrium forms a chamber into which the major systemic veins empty; caudal vena cava and cranial vena cava. The interior of the atrium is smooth.
Left Atrium
Similar to the right atrium, the left atrium receives the 4 pulmonary veins.
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