The effects of the pericardium on function of normal and enlarged hearts.

In summary, the pericardium is a membranous structure that surrounds the heart. Its physical properties are such that it is distensible when the total intrapericardial volume is small and inextensible when total intrapericardial volume is large. The pericardium serves to limit acute cardiac distention and to modulate the phenomenon of ventricular interdependence. It is a dynamic structure that, when subjected to chronic stretching--either due to the gradual accumulation of intrapericardial fluid or to cardiac enlargement--will grow to accommodate its contents, such that the working range of pressures between it and the surface of the heart is low. The precise level of cardiac distention that is necessary to engage the pericardium is unknown, but studies in normal and dilated hearts suggest that, at the upper end of the normal volume range of the heart, the intrapericardial volume is just sufficient to reach the noncompliant portion of the tissue's length-tension relation. Further studies are needed to determine whether this behavior represents a hemodynamic protective mechanism in normal animals.