A heart on the right can be more complex than it first appears.

To cite: Haththotuwa HR, Dubrey SW. BMJ Case Rep Published online: [please include Day Month Year] doi:10.1136/bcr-2013201046 DESCRIPTION At first glance these chest radiographs appear similar. Closer inspection suggests ‘dextrocardia’ (figure 1A) and ‘dextroposition’ (figure 1B). Confusing terminology is helped if the heart’s position within the thorax and point of direction of the apex is described. A heart and apex on the left is termed ‘levocardia’, a central heart with midline apex as ‘mesocardia’ and a right-sided heart and apex as ‘dextrocardia’. Dextroposition describes a heart on the right with an apex to the left, secondary to extracardiac causes (right lung hypoplasia, pneumonectomy or diaphragmatic hernia). In contrast, dextrocardia results from cardiac chamber disarrangement. ‘Dextrocardia’ (prevalence around 1/12 000) comprises three types, depending on the ‘situs’ (left or right orientation) of the atria and viscera. Normal orientation of the atria and viscera is termed ‘situs solitus’ (ie, left atrium, spleen and two-lobed lung on left). In ‘situs inversus’ the normal left and right orientation is reversed as a mirror image. When other viscera are involved, as in our patient (figure 1A), it is termed ‘situs inversus totalis’ (ie, spleen and stomach on the right and three-lobed lung on the left). In ‘situs ambiguous’ (prevalence around 1/ 20 000) the heart adopts left or right sidedness (isomerism). In left isomerism, both atria are morphologically left with multiple spleens, midline liver and both lungs are two-lobed. In right isomerism both atria are morphologically right with a midline liver, bilateral three-lobed lungs and no spleen. 3 Associated cardiac malformations with dextrocardia include atrioventricular septal defect, univentricular heart, transposition of the great arteries, atrial septal defect and anomalous pulmonary venous return.