READERS’ COMMENTS Constrictive Pericarditis: The Mitral Annulus Remains Paradoxical Because of its unique hemodynamic features, constrictive pericarditis may be identified using 2-dimensional and Doppler echocardiography. An important component of a “constriction-protocol” echocardiogram is the tissue Doppler assessment of the early diastolic mitral annular relaxation velocity (e0 ), which provides a noninvasive measure of left ventricular myocardial relaxation. The e0 velocity is reduced in most forms of heart failure related to myocardial disease, and the ratio of transmitral velocity (E) to e0 allows estimation of left ventricular filling pressure in many cases.1 Specifically, an E/e0 of 15 correlates with increased filling pressure, and an E/e0 of 8 to 15 is indeterminate with a wide range of possible filling pressures. In contrast, the e0 velocity and E/e0 ratio in constrictive pericarditis are opposite to what is expected. Rather than being reduced, the e0 is preserved or even increased in constrictive pericarditis.2,3 Accordingly, the E/e0 ratio does not have the expected relation with left ventricular filling pressure. We coined the term “annulus paradoxus” after observing an inverse relation between E/e0 and pulmonary capillary wedge pressure (PCWP), such that the lower E/e0 ratios correlated with higher filling pressure and vice versa. We recently evaluated e0 , E/e0 , and other echocardiographic variables in 130 patients with confirmed constrictive pericarditis (of mixed etiologies) compared with 36 patients with confirmed restrictive cardiomyopathy or severe tricuspid regurgitation.4 Differences between the groups were pronounced: the constriction group had an average medial e0 of 12.9 cm/s and an average E/e0 of 5.8, whereas the nonconstriction group had an average medial e0 of 7 cm/s and an average E/e0 of 16.1 (p