Left Isomerism left-sided isomerism anomaly in the asymmetry of the visceral paired organs (e.g. lungs) such that organs on the left and right side have the morphology normally seen on the left side of the body; this may also be associated with the presence of multiple spleens Fyler:192 Fyler:0192 MPheno.ontology MP:0000542 polysplenia syndrome (left isomerism) heterotaxia left isomerism; left-sided isomerism