Pericardial effusion without cardiac tamponade is defined by the detection of excessive pericardial fluid without clinical manifestations, particularly pulsus paradoxus (inspiratory decrease in systolic blood pressure greater than 10 mm Hg) and jugular venous distention. Nineteen consecutive patients without heart or lung disease who had pericardial findings and no evidence of tamponade were investigated by echocardiography: 14 with pericardial effusion and 5 with noneffusive ("dry") pericarditis. Patients with effusion had an inspiratory decrease in left ventricular ejection time (delta LVET) of 17.9 +/- 5.78 ms and an increase in preejection period (delta PEP) of 12.1 +/- 3.78 ms, each well beyond the respective respiratory changes measured in normal subjects. The 5 control patients with dry pericarditis had a mean delta LVET and delta PEP of only 8.0 and 7.0 ms, respectively. Of the 14 patients with effusion, 6 whose systolic pressure showed no respiratory change had mean delta LVET of 13.7 ms and delta PEP of 11.2 ms, comparable to the other 8 patients with effusion who had a respiratory change of 2 to 10 mm Hg. We conclude that although pulsus paradoxus was not present, excessive pericardial fluid is not physiologically inert. If a satisfactory echocardiogram is not available, exaggerated respiratory fluctuation in systolic time intervals may be evidence of excessive pericardial fluid.