9 Adult patients with large pericardial effusions (PE) demonstrated echocardiographic motion abnormalities of cardiac valves in systole. In 4 cases (Group I) the abnormal findings consisted of prominent systolic anterior movements of the mitral valve resembling those seen in idiopathic hypertrophic subaortic stenosis. In Group II (5 cases), typical mitral valve prolapse patterns with large posterior midsystolic displacements well below the C point were observed. Additional abnormalities in Group II included tricuspid valve prolapse patterns (4 cases), early systolic movement of the aortic valve toward closure (3 cases), midsystolic notching of the pulmonary valve (2 cases) and abnormal or attenuated motion of the aortic root in all patients. Marked decrease or resolution of PE resulted in complete disappearance of all the observed abnormalities. These findings appeared to be related to large fluid collections behind the left atrium and abnormal movement of the heart in the pericardial space. In the presence of PE, therefore, the echocardiographic observation of abnormal valve motion may not be clinically significant.