The functionally single fetal right ventricle demonstrates reduced longitudinal relative to circumferential contraction velocities and deformation, a pattern similar to the normal fetal left ventricle. Altered diastolic properties are also present, with greater reliance on atrial contraction for right ventricular filling. It is unknown whether the functionally single left ventricle (SLV) demonstrates similar altered deformation patterns and diastolic properties.Echocardiograms from 29 fetuses with SLVs were retrospectively compared with those from 48 controls with appropriately grown left ventricles. Ventricular function was assessed using Velocity Vector Imaging velocity, tissue deformation, two-dimensional, and Doppler flow parameters.Fetuses with functionally SLVs showed no difference in peak global left ventricular longitudinal velocity or displacement or strain, while global radial displacement was increased (P < .001). The ratio of longitudinal to circumferential deformation was also no different from that in controls. The SLVs showed increased diameters (P < .001) with normal lengths. Mitral inflow peak E-wave (P < .05) and A-wave (P < .0001) velocities were increased, with a reduced E/A ratio (P < .001). A-wave inflow fraction was also increased (P < .05), with no change in A duration. Although ejection time was no different, inflow duration was increased (P < .01) and there was a trend toward reduction of the Tei index (P = .07).The functionally single fetal left ventricle shows comparable changes to the single right ventricle, with a more spherical morphology and greater reliance on atrial contraction for ventricular filling than in controls. However, in contrast to the single right ventricle, the SLV had a normal longitudinal to circumferential deformation ratio with enhanced early diastolic filling.