This article discusses a thesis regarding the pathophysiology of constrictive pericarditis. The thesis is that there are two forms of constriction, one being elastic and the other more analogous to a rigid shell. The two forms of constriction are considered to cause different patterns of the diagnostic signs of constriction. The elastic form is similar to cardiac tamponade, and is associated with prominent paradoxical pulse and systolic descent in the venous pressure waveform. The rigid shell type has less prominent paradoxical pulse and a more conspicuous diastolic descent in the venous pressure waveform, often associated with an early diastolic sound (pericardial knock). Recognition of these two types of constriction may be helpful in clinical diagnosis and in understanding the pathophysiology of pericardial disease.