LETTERS TO THE EDITOR Diagnosis of Constrictive Pericarditis To the Editor:

The echocardiographic study by Veolkel and colleagues ' is a valuable contribution to the diagnosis and understanding of con-strictive pericarditis. One item, however, may be misinterpreted, since it was not discussed after it was described in the results. The authors found a range of pericardial thickness of 4-11 mm in their normal population. No doubt what they measured as "pericar-dium " was, indeed, 4-11 mm. However, I am certain the authors did not mean to indicate that the normal pericardium is that thick. Direct measurement of pericardial thickness, even at necropsy, is "tedious and difficult,"2 the most careful study yielding a mean thickness of 0.3 mm. Moreover, during growth and aging there are significant changes in thickness, elastic tissue composition and the physical characteristics of pericardial collagen.2 ' The difficulty of measurement is such that even otherwise Teutonically thorough studies seem to avoid it. ' It is likely that the resolving power o