Background Right ventricular volume overload (RVVO) occurring in conditions such as Ebstein's anomaly may result in depression of left ventricular ejection fraction (LVEF).This study tests this hypothesis by measuring LVEF in 10 patients with RVVO due to tricuspid valve resection for isolated tricuspid valve endocarditis and in 10 age-matched healthy persons.Methods and Results When the modified Simpson's rule was applied to echocardiographic images, LVEF for patients with RVVO measured significantly lower than for age-matched healthy subjects (51+-4% versus 60+-4%, P<.0001). Depression of LVEF does not result simply from reduced venous return to the left ventricle, since left ventricular end-diastolic volume was not significantly different between patients with RVVO and age-matched healthy persons (84+-26 versus 77+-20 mL, NS). Possible explanations for the depression in LVEF may relate to the decreased relative contribution of left atrial systole to left ventricular filling (demonstrated by transmitral pulsed Doppler) or to the mechanical effects of ventricular septal paradox (demonstrated by the abnormal leftward ventricular septal flattening and increase in short-axis cavity eccentricity at end diastole, which returns to normal at end systole) in patients with RVVO.Conclusions These findings suggest that surgical excision of the tricuspid valve results in isolated RVVO, which creates not only diastolic overload of the right heart but also depression of LVEF.(Circulation. 1994;90(part 2):II-209-II-213.)