degrees out of phase to the former These changes are similar to tamponade and in the absence of pericardial effusion have a high sensitivity and specificity for pericardial constriction Typically, mitral inflow velocity shows a restrictive flow pattern with E/A ratio greater than 0.8 and a greater than 25% increase during expiration compared to inspiration In patients with substantial fluid overload the pressure in the left atrium is markedly elevated This results in a transmitral gradient throughout respiration and may mask respiratory variation in mitral inflow velocity Preload reduction by diuresis can unmask characteristic respiratory variation in such cases.6,107,111,112 Similar to tamponade, the right ventricular filling is impaired during expiration and causes accentuated expiratory diastolic flow reversal in the hepatic veins (see Fig 57.5) Cardiac Catheterization Cardiac catheterization is the gold standard for the diagnosis of physiology of pericardial constriction While stroke volume is reduced, compensatory tachycardia maintains the cardiac output at rest The diastolic pressure in all the cardiac chambers and systemic and pulmonary veins is elevated (>20 mm Hg) and equal (