In 20 consecutive patients with echocardiographic pericardial effusions and no pulsus paradoxus or other signs of cardiac embarrassment the left ventricular ejection time fell (ΔLVET) during inspiration by 18.3 ± 2.47 (SE) ms, greatly exceeding mean inspiratory ΔLVET in normal subjects (7.0 ms). Median and mode ΔLVET were each 15.0 ms, with ΔLVET less than 10 ms and more than 25 ms in only 1 patient each. With a single exception, the magnitude of the abnormal ΔLVET was least in patients with minimal to small effusions. Ejection time indices were normal during expiration and low during inspiration, indicating diminished stroke volume during inspiration only. Thus, even without clinical and echocardiographic signs of cardiac compression, the presence of pericardial fluid clearly exaggerated respiratory effects on left ventricular function but not to the degree characteristic of overtly compressing (tamponading) fluid. The consistent exaggeration of ΔLVET during even small pericardial effusions is thus of physiologic interest and may be of diagnostic value.