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The pericardial sac encloses the heart, akin to the pleura that encloses the lungs. The pericardial sac has parietal and visceral layers separating a pericardial cavity lined with fluid.


The heart is enclosed within a three-layered pericardial sac that protects the heart, prevents overfilling, and produces a lubricating fluid. The three layers are as follows (Figure 4-1A and B):

  • Fibrous parietal pericardium. Tough external layer of connective tissue that surrounds the serous pericardium and prevents overfilling; it is attached to the central tendon of the diaphragm and blends with the tunica external of the great vessels of the heart.

  • Serous pericardium. Thin two-layered serous membrane is composed of an outer parietal layer and an inner visceral layer; produce pericardial fluid to line the pericardial cavity.

    • Parietal layer of serous pericardium. Covers the deep surface of the fibrous parietal pericardium; often referred to as the serous parietal pericardium.

    • Visceral layer of serous pericardium. Serous tissue that intimately follows the external contours of the heart surface; the combination of visceral pericardium with the underlying loose connective and adipose tissues is referred to as the epicardium.

    • Pericardial cavity. The space between the parietal and visceral layers of serous pericardium; contains serous fluid, which lubricates the heart to reduce friction.

Figure 4-1:

A. Coronary section through the thorax. B. Layers of the pericardial sac. C. Anterior (sternocostal) surface of the heart. D. Posterior (base) and inferior (diaphragmatic) surface of the heart. E. Atrioventricular (coronary) grooves in an anterior view. F. Atrioventricular (coronary) grooves in a posterior view.

The pericardial sac has two pericardial sinuses:

  • Transverse sinus. A horizontal space between the arterial ends of heart vessels anteriorly (ascending aorta and pulmonary trunk) and venous ends posteriorly (SVC); on each side the transverse sinus opens into the pericardial cavity.

  • Oblique sinus. A cul-de-sac space deep to the heart and surrounded by the reflection of the serous pericardium around the IVC and right and left pulmonary veins.

The pericardium has the following neurovascular supply:

  • Innervation. Parietal pericardium receives general sensory innervation from the phrenic nerve; visceral pericardium receives visceral sensory innervation from sympathetic nerves (to T1–T4 spinal cord levels) and vagus nerves (to medulla oblongata).

  • Blood supply. Primarily from the pericardiacophrenic vessels.



The heart has the following three layers (Figure 4-1B):

  • Epicardium. The outer layer of the heart consisting of loose connective tissue, adipose tissue and visceral pericardium.

  • Myocardium. The middle layer, consisting of cardiac muscle responsible for contraction of the heart.

  • Endocardium. The inner layer, consisting of endothelial cells that line the lumen of the four chambers.

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