Situs ambiguus or situs ambiguous (the former spelling is more correct etymologically, but the latter spelling is very common), also known as heterotaxy or heterotaxia, is a rare congenital defect in which the major visceral organs are distributed abnormally within the chest and abdomen.
The normal position of the organs is known as situs solitus; situs inversus is a condition in which the usual positions of the organs are reversed from left to right as a mirror image of the normal condition. If these are the two extreme positions on a continuum of asymmetric thoracic and abdominal organ formation, situs ambiguus covers everything in between. Both individuals with situs solitus and those with situs inversus generally have no functional impairments in their organ systems. In contrast, the mixing of organ asymmetries found in situs ambiguus often leads to severe and potentially fatal complications, usually of the heart or lungs. 
Classically, it comprises:
- Cardiac looping malformations – commonly Fallot’s tetralogy, transposition of the great vessels, pulmonary valve stenosis, and ventricular and atrial septal defects.
- Deranged abdominal organ asymmetry - the stomach and spleen are particularly prone to isolated reversal, and the stomach, liver, and a single adrenal gland are occasionally found in the midline.
- Organ malformations - chiefly asplenia-polysplenia, and more rarely a failure of the head of the pancreas to form, and horseshoe adrenals and kidneys.
- Rotation errors, causing volvulus and/or faulty peritoneal attachments.
More rarely, vascular abnormalities are found, including interrupted inferior vena cava, bilateral superior or inferior venae cavae, intrahepatic interruption of the inferior vena cava with connection to the azygos or hemiazygos veins, and aberrant portal veins.
Although its etiology is poorly understood, it has been found to be linked  to family history of malformations, and maternal cocaine use, suggesting both genetic and environmental factors play a role.
Genetic associations of heterotaxy include:
- Belmonte, Juan Carlos (June 1999). "How the Body Tells Left from Right". Scientific American: 46–48.
- Martínez-Frías ML (March 2001). "Heterotaxia as an outcome of maternal diabetes: an epidemiological study". American journal of medical genetics 99 (2): 142–6. doi:10.1002/1096-8628(2000)9999:999<00::AID-AJMG1139>3.0.CO;2-Z. PMID 11241474.
- Maeyama K, Kosaki R, Yoshihashi H, Casey B, Kosaki K (March 2001). "Mutation analysis of left-right axis determining genes in NOD and ICR, strains susceptible to maternal diabetes". Teratology 63 (3): 119–26. doi:10.1002/tera.1022. PMID 11283968.
- Kuehl KS, Loffredo C (November 2002). "Risk factors for heart disease associated with abnormal sidedness". Teratology 66 (5): 242–8. doi:10.1002/tera.10099. PMID 12397632.
- Kuehl KS, Loffredo CA (March 2003). "Population-based study of l-transposition of the great arteries: possible associations with environmental factors". Birth defects research. Part A, Clinical and molecular teratology 67 (3): 162–7. doi:10.1002/bdra.10015. PMID 12797457.
|In cognitive abilities||Geschwind–Galaburda hypothesis|
|In eyes||Ocular dominance|
|Handedness in boxing||Southpaw stance||Orthodox stance|
|Handedness in people|
|Handedness related to|
|Handedness measurement||Edinburgh Handedness Inventory|
|In major viscera||Situs solitus||Situs ambiguus||Situs inversus|