Heterotaxy (heterotaxia) is a clinically and genetically heterogeneous disorder which may include organ isomerism, failure of internal organs to lateralize or failure of paired organ primordia to regress. Situs inversus is the mirror image of normal organ arrangement, while situs ambiguous is any abnormal arrangement of abdominal organs. Also included in the clinical spectrum of heterotaxy are cardiac defects including atrioventricular septal defect (AVSD), common atrial septal defects (ASD), malposition or transposition of the great arteries (TGA), Tetralogy of Fallot (TOF), dextrocardia, and patent ductus arteriosis (PDA). This class of cardiac defects accounts for 3% of all congenital heart disease. Severity of these conditions ranges from asymptomatic to life-threatening. Prevalence is estimated to be 1/10,000 live births with a 2:1 ratio of affected males to females based on a study with strict inclusion criteria for heterotaxy. For more information regarding genetic testing for Heterotaxy, call GeneDx and ask to speak with a cardiovascular genetic counselor.