Pericardium. The pericardium is a very thin membrane that surrounds the heart. When the pericardium becomes inflamed from various causes, it can become thickened and can even calcify and severely impair heart function.
As it sounds. The pericardium is the fibrous covering that surrounds the heart. On echo, ct or mri, it can appear to be thick and is read as such but there is no clinical significance unless it causes abnormal physiology called constrictive pericarditis. CP results in a syndrome which is similar to congestive heart failure.