pericardium
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Heart
, river, United Statesheart
, in anatomy
heart, muscular organ that pumps blood to all parts of the body. The rhythmic beating of the heart is a ceaseless activity, lasting from before birth to the end of life.
Anatomy and Function
Cardiac Cycle
Advances in Cardiology
One of the important advances in cardiology is the artificial pacemaker used to electrically initiate a normal heartbeat when the patient's own pacemaker is defective (see arrhythmia); it may be surgically implanted in the patient's body. Similarly, an internal defibrillator may be implanted to deliver an electrical shock to the heart in order to stop certain forms of rapid heart rhythm disturbances. Another familiar tool of the cardiologist is the electrocardiograph (EKG), which is used to detect abnormalities that are not evident from a physical examination (see electrocardiography).
One of the most important advances in heart surgery during the 1960s was the transplantation of the healthy heart immediately after the death of an individual (the donor) to a recipient suffering from incurable heart disease (see transplantation, medical). In the 1980s new advances in the design and construction of an artificial heart—both the entire organ and such parts as the valves and large blood vessels—showed some promise in treating cardiovascular disease (see heart, artificial), but the limited success that has characterized artificial heart implantation thus far has led many experts to question the efficacy of such measures. Although the artificial heart has often been used as a temporary measure until a permanent human donor heart can be located, a number of recipients have not fared well, even for a limited duration. In addition, it is often unclear how long the recipient will have to wait for a donor. Proponents of the artificial heart hope that technological advances will allow the permanent replacement of human hearts with artificial ones.
See circulatory system; heart disease.
Bibliography
See J. Peto, The Heart (2005).
Pericardium
the closed, saclike structure surrounding the heart in vertebrate animals and in man. The pericardium is an isolated part of the secondary body cavity, the coelom. It consists of two layers: an external, parietal layer—the pericardium proper—and an internal, visceral layer—the epicardium. The pericardium proper consists, in turn, of an internal, serous layer and an external, fibrous layer. The epicardium, being an external membrane of the heart, directly covers and is fused to the heart muscle (myocardium). In the region where large blood vessels enter and leave the heart, the epicardium is turned back and is continuous with the pericardium proper. Between the pericardium layers is a slitlike cavity containing a small quantity of transparent pale-yellow serous fluid. The pericardium contains blood vessels, lymphatics, and numerous nerve endings and is surrounded by areolar connective tissue. It has many receptors, whose stimulation causes hemodynamic and respiratory changes.