The ratio of early transmitral flow velocity (E) to mitral annular velocity (E′) is considered a predictor of pulmonary capillary wedge pressure (PCWP). In a previous small study, the paradoxical relation between PCWP and E/E′ ratio has been described in patients with constrictive pericarditis (CP). We sought to test this paradoxical relation in a larger cohort. We retrospectively identified 49 patients with surgically confirmed CP (40 men; mean age 61 ± 10 years) who underwent right-sided cardiac catheterization with PCWP measurement, preceded by an echocardiographic study. Of these, 48 patients underwent either computed tomography or magnetic resonance imaging to measure pericardial thickness on the lateral side of the left ventricular wall. Mean interval time between echocardiogram and right-sided cardiac catheterization was 1.5 ± 3.8 days. There were no significant correlations between mean, medial, or lateral E/E′ and PCWP (r = −0.17, 95% confidence interval [CI] −0.43 to −0.12; r = −0.17, 95% CI −0.43 to −0.12; and r = −0.12, 95% CI −0.39 to −0.17, respectively). Similarly, there was no correlation between mean E/E′ and brain natriuretic peptide (Spearman r = −0.17, p = NS). Patients with increased pericardial thickness (defined as >4 mm) had both lower lateral peak systolic annular velocity (S′) and lower lateral S′ integral (7.8 ± 2.4 vs 9.6 ± 2.4, p = 0.02 and 13.2 ± 4.2 vs 15.9 ± 4.7, p = 0.04, respectively). In patients with CP, there were no correlations between septal, lateral, or mean E/E′ and PCWP. In conclusion, E/E′ is not predictive of filling pressures in patients with CP, and perhaps the “annulus paradoxus” phenomenon should be revisited. The relation between the mitral annular velocity and thickness of the parietal pericardium may affect this phenomenon.