OBJECTIVE Neonatal congenital tricuspid valve (TV) dysplasia and/or displacement (Ebstein's malformation) with severe tricuspid regurgitation (TR) is a challenging condition in which outcomes are frequently poor. Little is known about left ventricular (LV) function during the perinatal period in patients with congenital TV disease. The objective of this study was to evaluate LV function in fetuses with congenital TV anomalies associated with significant TR. METHODS Serial fetal echocardiograms in 16 fetuses with congenital TV dysplasia and/or displacement (five neonatal survivors and 11 fetal or neonatal deaths) were reviewed. LV stroke volume, LV end-diastolic volume (LVEDV), LV end-diastolic dimension (LVIDd), the LV eccentricity index, thoracic and cardiac areas and the cardiothoracic area ratio (CTAR), the right atrium area index, and LV longitudinal strains were compared according to gestational age and clinical outcome. RESULTS The gestational age-adjusted LVEDV (Z-score) was lower in late gestation (-1.2 ± 1.2 at last examination ≥ 28 weeks) than earlier in gestation (0.3 ± 1.5 at last examination < 28 weeks) and LV output was lower than reported late-gestation normal values. LV short-axis dimension correlated with LV volume and CTAR. LV mid-septal strain was lower than the normal average of fetal mid-septal strain and correlated with the LV eccentricity index. Among these parameters, only the LV eccentricity index differed between survivors and non-survivors. CONCLUSION LV function and anatomy are abnormal in fetuses with severe congenital TV anomalies and may be important contributors to outcome.