The differential diagnoses of cardiac tamponade, constrictive pericarditis, restrictive cardiomyopathy, effusive-constrictive pericarditis, and right ventricular infarction are often difficult because of the right ventricular diastolic dysfunction that frequently dominates the clinical picture in these disorders. In cardiac tamponade, key diagnostic signs are pulsus paradoxus, evidence of pericardial fluid by echocardiography or computed tomography (CT), and equalization of diastolic pressures. In constrictive pericarditis, prominent findings include Kussmaul's sign, evidence of pericardial calcification, equalization of diastolic pressures, and the square-root sign. Restrictive cardiomyopathy may be distinguished from constrictive pericarditis by the absence of pericardial calcification and, in amyloidosis, by a speckled pattern on two-dimensional echocardiogram and abnormal technetium Tc 99m pyrophosphate uptake during radionuclide examination. With effusive-constrictive pericarditis, hemodynamic signs of tamponade change to constriction with pericardial aspiration. In right ventricular infarction, constrictive-restrictive signs, as well as pulsus paradoxus, may be present. History and/or objective evidence of diaphragmatic left ventricular myocardial infarction