This chapter compares ultrasonic (echocardiographic) cuts with those made on heart specimens to define the morphological features of Isomerism. There are two schools of thought about this disorder. Ours, headed by Professor Robert H. Anderson, regards the primary feature of this syndrome to be the morphology of the atrial appendage, i.e., the pectinate musculature of the atrial appendages. The other school, headed by Dr. Richard van Praagh, considers the syndromes to be part of a systemic heterotaxy disorder. Heterotaxy options are either Polysplenia or Asplenia, or Situs Ambiguous when the atrial morphology cannot be identified.